[McMaster]

It is called sleep paralyzis (I think), and I've had it several times. This happens when your brain is still in sleep mode but is also little awake. Usually person can see surroundings, but can't move their body or talk. Usually this is accompanied with sence of other presence in the room and some people even see things. Also sensation of pressure on the chest is reported. Me personally one time realized what was going on, and I thought that I'll see what happens if I just let it keep going. Soon I started to have sensation that my lips were being sucked in my mouth, like Homer Simpsons lips when he eats something tangy. That felt uncomfortable, so I decided to wake myself up.
First time this happened it did frighten me a little bit because I didn't know what was going on. Oh, and I think it is pretty common too.