ButtLight,
So sorry to hear what your son experienced. As it was at night, and he woke up, it could have been a night terror, they can be very real and vivid, and it is possible to describe things in detail. This kind of thing has happened to me too.
On the other hand, if he switched on the light and the "thing" disappears, then it may be worth investigating further.
I do believe in the existence of fallen angels, for some strange reason they delight in scaring the crap out of people.
some may mock the existence of spirits, but then they will have no trouble believing in aliens.
You could try sleeping in the same room so you can both be present, should anything happen.
Re: the camcorder advice some have given, this usually doesn't work from what I've heard, they don't like being recorded.