Spontaneously falling asleep isn’t the only indicator you or someone you love might have the condition, reports Prevention.

In adults, narcolepsy is associated with sudden weakness or loss of muscle tone—often in response to laughter or strong emotion. Basically, a person’s body goes limp or loses strength.

But in kids, narcolepsy can cause some “active” movement patterns, rather than a loss of muscle tone. Raised eyebrows, grimacing, strange mouth and tongue movements, and body swaying—especially when a child is feeling strong emotion—are all symptoms of narcolepsy, according to a 2011 study in the journal Brain.