There's a very real phenomenon called 'sleep paralysis', which is completely normal and sounds like what you describe. It is a normal part of the sleep cycle of which we are usually unaware, but for some reason the part of our brain that is usually "asleep" at that time is awakened and we become conscious of it.

It started happening to me in my early twenties and scared the hell out of me! It usually happens just as I am falling asleep but I remain calm and tell myself that I will be able to open my eyes and will be able to move in a minute or two, and to just keep breathing, that I'm okay. Occasionally I felt like I was being suffocated too (maybe my face was buried in the pillow partially?) but usually I can breath normally and just focus on that and try to move a finger, then the hand, etc. Before I know it I'm awake and usually drift right to sleep. It seems to happen to me when I'm under a lot of stress (ha ha) and am very sleep deprived.