Sleep paralysis

When people are dreaming, their muscles do not move, even if in their dream they are moving.  This is a natural process that prevents people from actually performing the movements they make in their sleep.

In general, people are not aware of this inability to move, as it usually stops as soon as they wake up. People suffering from sleep paralysis wake up and find that they are unable to move. This is because the paralysis has not stopped. Usually it lasts for only a few minutes, and people have said they feel a "presence" or "ghost" during it.

 Possible causes 
Little is known about the physiology of sleep paralysis. However, some have suggested that it may be linked to post-synaptic (neurons sending signals to other neurons) inhibition (restraint) of nerves in the pons (back) region of the brain. In particular, low levels of melatonin may stop the depolarization current in the nerves, which stops stimulation of the muscles.

Hallucinations of ghosts, demons and Out of Body Experiences during sleep paralysis may be caused by a part of the brain called the parietal lobe (top-middle part of the brain), and by neurons known as mirror neurons.

Studies suggest that many people get sleep paralysis at least once in their lives. People who have narcolepsy often get it much more. Many people try to induce sleep paralysis, to have an Out of Body Experience. 

Some report that various factors make paralysis and hallucinations happen more. These include:
 Sleeping on your back
 Irregular sleeping schedules; naps, sleeping in, sleep deprivation
 Increased stress
 Sudden changes of lifestyle or environment
 A lucid dream just before it
 Medium to long-term imagining of involuntary movements with your eyes closed before sleep.

 Treatment 
There are few treatments available for sleep paralysis. One treatment is called Meditation-Relaxation Therapy. The treatment includes four steps: (1) one should close their eyes and remind themself that the experience is not dangerous in any way, and it is common around the world; (2) and that since it is not dangerous, they should not be afraid as that will only make the experience worse. (3) They should then focus very strongly on a positive thought or mental image (meditate); (4) and also relax their muscles and avoid movement. 

 References 

Other websites
The Guardian - The waking nightmare of sleep paralysis
On the Neuroscience of Sleep Paralysis 

Category:Symptoms