Sleep paralysis is a temporary inability to move or speak that occurs when falling asleep or waking up. During an episode, the person is conscious and aware of their surroundings but finds themselves completely unable to move any part of their body, typically for a period of seconds to a few minutes. The experience is often accompanied by a feeling of pressure on the chest, a sense of an unseen presence in the room, and vivid, sometimes frightening hallucinations. Sleep paralysis occurs during the transition between wakefulness and sleep, when the brain is shifting in or out of REM sleep. During REM sleep, the brain temporarily paralyzes the body’s voluntary muscles — a mechanism called REM atonia — to prevent the sleeper from acting out their dreams. Sleep paralysis occurs when this paralysis persists briefly after the person has become conscious. While the experience can be deeply unsettling, sleep paralysis is generally harmless. It is surprisingly common — studies suggest that up to 40 percent of people experience it at least once in their lifetime. It occurs more frequently in people who are sleep-deprived, have irregular sleep schedules, suffer from narcolepsy, experience high levels of stress, or sleep on their back. Episodes of sleep paralysis are typically short-lived and end on their own. Trying to wiggle a finger or toe, or having a sleep partner touch the person, can help end an episode. To reduce the frequency of sleep paralysis, improving sleep habits is recommended: maintaining a consistent sleep schedule, getting adequate sleep, reducing stress, and avoiding sleeping on the back. If sleep paralysis occurs frequently or causes significant distress, consulting a doctor or sleep specialist is advisable.