Many people experience sleep paralysis. The true causes for it are still largely unknown. There are speculations that it is caused by great bodily stress or some even believe it is a condition caused by aliens when they are attempting to do something to the body. Astral projection or just the Chakras of the body at work can also be the underlying causes.
The symptoms of sleep paralysis are similar to the symptoms of astral projection, electrical pulses are felt throughout the whole body just when the soul is about to leave the body. One will either feel total loss of control of the body's movement or he will feel electrical pulses throughout his whole body causing paralysis.
I myself have frequently been experiencing sleep paralysis. Sometimes I can feel an evil presence beside my body when I am experiencing it. In that case I always try to come out of the paralysis immediately. I use my Mind's will power to resist and will myself to regain my body's control and I have always been successful in doing so. The last time I felt a strange presence beside my body and I used a chant/prayer/spell that I learnt from the "Charmed" TV series which I feel is logical and has powerful effects when saying it.
I didn't use any will power nor any strength on my part to come out of the paralysis, I only said in my Mind "I am Light, I am One too strong to fight" just once and the presence left me and I immediately regain total control of my body's functions. It was amazing how quickly it worked. The "I am" is the name of God as He told us from the phrase "I AM that I AM". Light is the body and spirit's Aura and by acknowledging that it exists, one can use it to protect against evil. The phrase "I am Light" means to say one calls upon the power of God's aura, which is also in us all, and "I am one too strong to fight" meaning that one acknowledges that one and his aura is sovereign over anything else.
So remember if whenever you feel any uncomfortable or evil presence while sleeping, do not be afraid, be strong and resist it.