Sounds a lot like something that happened to me once, Amy. I was having something of a nightmare, got out of bed, scrabbled for the light switch, fell through the door, and found myself in the hallway going "Um...whoa. That ain't right."
And for several years, I thought it was astral projection, too. I believed it was. Ooo! I can astral project! I've done it! I am in touch with the astral!
Then I started having it happen a lot, and I learned about sleep paralysis.
Sleep paralysis is a condition that afflicts a lot of us occasionally, and some of us a lot. I get it a lot. Most commonly, I think I've woken up, I get up, I walk around, and it's only when I see something in the environment that's completely out of kilter (i.e. "Why is my deck covered in owls?") that I realize I'm still asleep. This is known as a "hypnogogic hallucination" and it can happen four or five times in the course of my waking up if I've got a bad case of it. Occasionally, however, I get sensations of floating or of leaving my body. Both of these are fairly common occurences among people suffering sleep paralysis. (There are a few others, like a sense of an intruder, but thankfully, I hardly ever get that one.)
The thing is, it's really, REALLY easy to believe this is not like dreaming, because the quality of a hypnogogic hallucination can be bloody amazing. I've done LSD and mushroom both, and even though both experiences are called "hallucinations" they're nothing even close. A hypnogogic hallucination can be just about bloody perfect. You feel your body. You feel it MOVING. I can wave my arms and feel them waving, even when they're really tucked down at my sides under the blanket. It's really quite an extraordinary experience. People afflicted by it often say "It wasn't like a dream!" when they try to claim that they're astrally travelling or being abducted by aliens* or whatever. And in that, at least, they're quite correct--sometimes it really isn't like a dream. As subjective reality goes, it's a whole 'nother kettle of fish.
However, I'm not travelling astrally or anything else when this happens. As I understand the science, (and no neurosurgeon am I!) I'm suffering from a brief malfunction of the part of my brain that keeps me from acting out stuff I'm dreaming--I'm still paralyzed, but my brain's mostly awake, and in response to the orders to get up and walk around, it's getting caught in weird feedback loops and generating something like dreaming, so that I think I'm getting up and walking around, but I'm still stuck in bed.
Happens to me about once every two or three weeks. These days, once I realize what's happening, my usual response is "Aw, hell, sleep paralysis AGAIN."
So, I do know exactly what your experience felt like, and I can sympathize. There was a time when I thought it must have been astral travel too, because gee, how cool would that be? A whole astral dimension! And I could go there! Awesome!
But...there really isn't one. It's a sleep disorder, and a pretty common one. Lots of people have it. This is disappointing, I know, and I don't expect you to accept it--I wanted to cling to the notion of astral travel for years myself. However, just because a website on the internet says "There's an astral dimension!" doesn't mean there is one. Ask yourself "How do they prove there's an astral dimension? How can *I* prove there's an astral dimension?" Try to think of a way to test whether or not astral travel is happening. Ask yourself why you should believe this website, in particular, and not, oh, the ones who claim toothpaste is a tool of the Rosicrucian conspiracy. What proof of their claims does this particular website have that makes them credible, other than the fact that you want to believe in astral projection?
If you want to test this for yourself--and I highly suggest you do!--then try one of the tricks various people have suggested with the cards or throwing a pair of dice, or opening a book on top of a high bookcase.
If you don't want to test it for yourself, it's probably for the same reason I never wanted to--I was afraid I'd prove myself wrong, and I really wanted to believe--and I can only offer my sympathy.
If you'd like read more about sleep paralysis, including the common associated sense of an out of body experience, and to help science learn more about sleep paralysis by recounting your experience,
http://watarts.uwaterloo.ca/~acheyne/S_P.html has some good information, and an on-line survey form where you can document your experience for their research.
*Oddly enough, I usually find myself squinting in bright light during the course of the hallucination, but waking up, it'll be quite dim. The bright lights are apparently a pretty common symptom, and probably part of the reason for the abductee insistence on that.