I feel someone sitting beside my bed when I sleep. I can't talk or move. Why?

This is called ghost bed in folk and nightmare in medical field. Pathologically, when you suddenly wake up during sleep, when your muscles and nerves are not awake, you will be conscious and unable to move. This is called a nightmare.

Nightmares can be said to be a normal psychological phenomenon, which has nothing to do with ghosts. Usually, it is more likely to happen under the conditions of great pressure, excessive fatigue, abnormal work and rest, insomnia and anxiety. Science shows that nightmares are caused by transient cerebral ischemia during sleep. When transient cerebral ischemia occurs during the day, people will have terrible symptoms such as dizziness, palpitation, chest tightness, black eyes, tinnitus and various neurological disorders.