akanchababu,
don't worry it's common.
it's called sleep paralysis.
your mind is very powerful thing, it can create lot of things beyond our imagination. I don't know how did you live your life this month but there are some reasons behind it:

-lack of sleep
-anxiety
-depression
-poor nutrition
-tiredness and fatigue
-health related issues

If I were you, I would check blood pressure,
I would start taking supplements, esp choline & Inositol for nervous system.
Take enough rest, medidate, pranayam yoga and exercise.

It has happened to me as well,.. I'm pretty much sure you close your eye when that happens otherwise, you'd see knarly creature sitting in your chest. You don't need to freak out , it's normal and there is nothing evil. Like I said, i'ts your mind that is conjuring up all these. Your mind needs some time free of tension and you can achieve with meditation and some pranayama. Many people hear voices when that happens, with buzzing sound in the ear, body totally becoming stiff, can't move a bit and stuff.. it's normal..

but if you need immediate relief, go and get some antihistamine, just before sleep, take it with water, and see how you sleep? It's not a sleeping pills,it's harmless just don't make it habit. you'll sleep like a baby. After a day or two, you'll get back to your normal routine