Tests such as overnight sleep studies, manometry, pH monitoring, or electroencephalography can help physicians determine if patients complaining of nocturnal panic attacks have possible sleep disorders.

By Regina Patrick, RPSGT

If a person suddenly awakens from a deep sleep with chest pain and breaths can be taken only in short, unfulfilling gasps, it can leave that person feeling suffocated and dizzy. Their fingers will tingle and slowly become numb and a rush of anxiety arises as the realization occurs that this could be a heart attack and a prelude to dying. This person may go to an emergency department only to be told that these are symptoms of a panic attack.

During a panic attack, people have at least four of the following symptoms: heart palpitations or pounding heartbeat; sweating; shakiness or trembling; hyperventilation as a result of feeling suffocated; fear of losing control; chest pain; sensation of choking; nausea or abdominal distress; dizziness, fainting, or lightheadedness; hot flashes or chills; numbness or tingling sensations in the extremities; sudden rush of fear, sense of impending doom or death, or desperate urge to flee; and/or a sense of being detached from self or reality. These symptoms arise suddenly even though there is no actual threat and subside in about 10 to 20 minutes.

Panic attacks that awaken people from sleep (nocturnal panic attacks) can actually be a sign of a sleep disorder. Obstructive sleep apnea (OSA), sleep-related gastroesophageal reflux disease (GERD), sleep-related laryngospasms, and sleep-related seizures can cause people to wake from sleep with symptoms of a panic attack.

Obstructive sleep apnea
In OSA, the muscles of the upper airway relax too much during sleep and close off the airway. Blood oxygen levels fall since a person cannot breathe. Once oxygen falls to a certain level, people arouse for a few seconds. This arousal restores muscle tone to the airway and they are able to take some quick, deep breaths. People usually snore loudly as they are taking these breaths. Their hearts race quickly to supply oxygenated blood throughout the body.

In these few seconds of arousal, people may be aware of being choked and may feel their heart racing while struggling to breathe. These sensations can cause panic and create a feeling of dying. If people are unaware that their breathing has stopped periodically during sleep or that they snore loudly, they may believe that panic attacks are waking them from sleep rather than the possibility of OSA.

Gastroesophageal reflux disease
In GERD, the lower esophageal sphincter does not work properly to prevent digestive fluids from flowing backward from the stomach into the esophagus. This backflow is called reflux. In some people, digestive fluids can flow from the stomach all the way up to the throat. The acidity of the fluids causes a burning sensation or pain in the esophagus and throat since these areas do not have the same protective covering as the stomach. The refluxed fluids can leave a sour taste in the mouth.

Reflux that occurs during sleep can cause a person to wake up with a sensation of burning or pain in the chest. This discomfort can cause a reflexive increase in respiration, forcing the person to breathe in short gasps. An episode of reflux can create anxiety and a fear that this might be a heart attack.

Objective tests such as manometry and pH monitoring may need to be done to determine if a person has GERD. Manometry measures the pressure exerted by the esophagus and can determine if the pressure exerted by the lower esophageal sphincter is sufficient to prevent reflux. Monitoring the pH of the lower esophagus can pick up the presence of acidity from digestive fluids flowing from the stomach into the esophagus.

Sleep-related laryngospasm
A laryngospasm is the sudden contraction of the vocal cords. This contraction causes the vocal cords to come together and block the airway. When a laryngospasm happens during sleep, a person awakens unable to inhale or exhale. A few seconds later, the airway opens partially. This causes a high-pitched sound when inhaling. Within approximately 1 minute, the laryngospasm ends and the person is able to breathe normally. This can cause fear and panic during the time a person is struggling to regain his breath.

Sleep-related laryngospasms tend to occur in middle-aged men. They happen for unknown reasons, although irritation to the vocal cords (from reflux or infection) or a low calcium level can be a cause.

Sleep-related seizures
Some people have seizures only during sleep. Seizures that begin in the temporal lobe can give sudden rise to feelings of doom, fear, or panic. Depending on the path in which it travels in the brain, a temporal lobe seizure can produce physical symptoms matching those of a panic attack including hyperventilation, sweatiness, increased heart rate, tingling, chest pain, or a detached feeling from self or surroundings.

An automatism is an uncontrolled, aimless movement of a part of the body such as finger twitching and leg jerking. These movements can occur during a temporal lobe seizure but do not occur during a panic attack. A person who has automatism with what appears to be a nocturnal panic attack may be having a sleep-related seizure.

Although sleep disorders can entail symptoms of a panic attack, they cannot explain all nocturnal panic attacks. What sets a nocturnal panic attack into motion is often unknown. Physiological and psychological factors play a role, but scientists are not sure if nocturnal panic attacks can be blamed mostly on physiological or psychological causes.

Faulty chemoreceptors, ventilation, and brain receptors have been investigated as physiological reasons for panic attacks. An inability to rest and conditioning have been investigated as psychological reasons for panic attacks.

In the 1950s, research by German and Belgian scientists1 noted that acidifying the cerebrospinal fluid affected respiration rate in laboratory animals. At the time, scientists hypothesized that the pH of the cerebrospinal fluid influenced the body’s sensitivity to CO2.

With this hypothesis in mind, German researcher Hans Loeschcke and American researcher Robert Mitchell2 independently worked to find the area of the brain thought to be sensitive to CO2. In 1960, Loeschcke came to America and joined forces with Mitchell to look further into this area. They found that a certain area in the medulla was sensitive to CO2.

The interplay between the CO2 chemoreceptors in the medulla and the carotid body controls breathing rate. The carotid body, nestled in the junction between the internal and external carotid artery, contains chemoreceptors that are sensitive to blood levels of CO2 and O2. This information is relayed from the carotid body to the medulla through the autonomic nervous system. When the blood oxygen level is low, the medulla then triggers a person to breathe deeply and fast (hyperventilation reflex). When the oxygen level is high, the medulla triggers slower breathing.

This interplay may be altered in people with panic disorder. Supporting this hypothesis is the fact that levels of carbon dioxide are higher than normal during sleep in people who have panic attacks.3 This retention of CO2 occurs even though the person does not have sleep apnea or other respiratory problems. Scientists have no explanation for this finding.

The “false suffocation alarm” theory proposed by Donald F. Klein4 in 1993 is widely accepted by scientists. This theory proposes that the brain misinterprets the level of CO2 as excess, creating a sense of suffocation. This in turn causes a person to hyperventilate and have other symptoms of a panic attack.

Supporting this theory is the fact that panic attacks can be induced in people with panic disorder by inhaling CO2. Higher levels of CO2 are needed to create the same sense of suffocation or hyperventilation in people who do not have panic disorder. In keeping with the idea of false suffocation, Battaglia5 suggests that panic at-tacks may be partially controlled by CO2-sensitive cholinergic receptors in the brain. The author suggests that the function of these receptors may be altered so that less CO2 is needed to cause a sensation of suffocation and set off a panic attack.

In one study, Battaglia et al6 investigated the ability of two anticholinergic drugs—biperiden hydro-chloride and pirenzepine hydrochloride—to lessen the panic response. These drugs block the ability of cholinergic receptors to use the neurotransmitter acetylcholine. Biperiden acts on cholinergic receptors in the brain while pirenzepine acts on cholinergic receptors outside the brain.

Two hours after taking either one of the drugs or a placebo, subjects inhaled an oxygen/carbon dioxide mixture (65% O2/35% CO2) to induce a panic attack. The authors found that subjects who had taken biperiden had reduced symptoms of panic (hyperventilation and anxiety) while symptoms were not reduced in subjects who had taken pirenzepine or the placebo. These results validated their hypothesis that cholinergic receptors in the brain play a role in panic attacks.

Craske et al7 note that people who have panic attacks seem to respond to loss of vigilance with panic. That is, when the person is in a deep relaxed state such as meditation or sleep, the relaxation itself causes the person to feel symptoms of panic. In one study7 the authors found that people with nocturnal panic attacks began to have symptoms of panic or felt more anxious when doing a meditative relaxation when compared to people who had daytime panic attacks.

In this study, a pretest questionnaire was given to those with nocturnal panic attacks who tended to answer affirmatively to questions such as “I find it hard to just let go,” “I feel uneasy when I try to relax,” and “I’m apprehensive when I’m sitting around doing nothing.” Craske et al7 term this inability to relax “a fear of loss of vigilance.” By this, they mean that people with nocturnal panic attacks may fear that when they are relaxed, they will be unable to respond appropriately and therefore are unable to protect themselves from threatening stimuli. Since sleep represents the ultimate relaxation and vulnerability, the fear of loss of vigilance would make a person prone to nocturnal panic attacks. Another possibility they suggest is that sleep-related cues (such as arousals) may become associated with panic attacks. This means that panic attacks may be a conditioned response in some people.

When a person complains of nocturnal panic attacks, doctors rule out disorders that commonly mimic panic disorder such as hyperthyroidism, post-traumatic stress disorder, and hypoglycemia; however, doctors frequently do not consider that sleep disorders can be a possible cause of nocturnal panic attacks. Tests such as an overnight sleep study, manometry, pH monitoring, or electroencephalography may be needed to rule out this possibility.

Regina Patrick, RPSGT, is a contributing writer for Sleep Review.

1. Sloan EP, Natarajan M, Baker B, et al. Nocturnal and daytime panic attacks—comparison of sleep architecture, heart rate variability, and response to sodium lactate challenge. Biol Psychiatry. 1999;45:1313-1320.
2. Battaglia M. Beyond the usual suspects: a cholinergic route for panic attacks. Mol Psychiatry. 2002;7:239-246.
3. Battaglia M, Bertella S, Ogliari A, et al. Modulation by muscarinic antagonists of the response to carbon dioxide challenge in panic disorder. Arch Gen Psychiatry. 2001;58:114-119.
4. Craske MG, Lang AJ, Tsao JCL, et al. Reactivity to interceptive cues in nocturnal panic. J Behav Ther Exp Psychiatry. 2001;32:173-190.

Additional Reading
Edlund MJ, McNamara ME, Millman RP, Sleep apnea and panic attacks. Compr Psychiatry. 1991;32:130-132.

Mellman TA, Uhde TW. Patients with frequent sleep panic: clinical findings and response to medication treatment. J Clin Psychiatry. 1990;51:513-516.

Norton GR, Norton PJ, Walker JR, et al., A comparison of people with and without nocturnal panic attacks. J Behavior Ther Exp Psychiatry. 1999;30:37-44.

Severinghaus JW. Hans Loeschcke, Robert Mitchell and the medullary CO2 chemoreceptors: a brief historical review. Respir Physiol. 1998;114:17-24.

Shapiro CM, Sloan EP. Nocturnal panic—an underrecognized entity. J Psychosom Res. 1998;44:21-23.

Thompson SA, Duncan JS, Smith SJM, Partial seizures presenting as panic attacks: partial seizures should be considered in the differential diagnosis of refractory or atypical panic attacks. BMJ. 2001;322:864.

Waldrop TG, Rybicki KJ, Kaufman MP, Ordway GA. Activation of visceral thin-fiber afferents increases respiratory output in cats. Respir Physiol. 1984;58:187-196.