How is the terrible sleep paralysis produced?

have you ever had such,when you are asleep,you consciousness suddenly becomes clear.but your body is paralyzed,such experience can be horrible,because he often has sleep hallucinations together.you'll see some at this time something you don't normally see ,there will also be a feeling of suffocation,you can even feeling his Respiration and body temperature,in fact,this is sleep paralysis.
So why do we experience sleep paralysis?

some people are insomnia pressure depressed or specific drugs to trigger it .when it happens,the key is net to confront him,to try to relax and control ,Calm down,try to move your fingers and toes ,because of the sensation of these areas not completely paralyzed,you con wake up.