Sleep paralysis is a condition

 People when falling asleep temporarily experience an inability to move. It is a transition state between wakefulness and rest characterized by complete muscle weakness. It can occur at sleep onset or upon awakening, and it is often associated with terrifying visions, such as an intruder in the room, to which one is unable to react due to paralysis. Sleep paralysis has been linked to disorders such as narcolepsy, migraines, anxiety, and obstructive sleep disorder.

Cause

Sleeping in the supine position is believed to make the sleeper more vulnerable to episodes of sleep paralysis because in this sleeping position is possible for the soft palate to collapse and obstruct the airway. > siliguri