Inverse: An expert explains why people are having weird dreams after getting their shot.

Chelsie Rohrscheib, a sleep expert and neuroscientist with Tatch Health, has heard “many reports” of people having changes in their sleep. “Common changes [post vaccination] include increased or decreased sleep duration, issues falling asleep or staying asleep, and changes in dreams,” she tells Inverse.

None of these reports are “surprising from a medical and scientific perspective,” she says. To understand why people may have strange or vivid dreams after getting the Covid vaccine, she says, it’s useful to understand why we sleep more when we’re sick.