This description might be confusing term-wise but it is as I felt it then, many years ago, without knowing anything about OBE. I thought I was just in some hypnotic like state or deep meditation.
It was at night, I was fully aware of everything, laid in the bed and I got into that altered hypnotic state I knew, because I wasn't really tired and was just experimenting with it and curious. After I stopped being so disturbed by the feeling of that altered state, I thought that I will try to absorb some energy from the universe through my whole body when I felt so tuned in. (I knew a bit about chakras and aura, I could see the light a few cm around everyone when they were against light background and I just started to be interested in yoga.) I laid on my back in the savasana (yoga position with the spread arms and legs, palms up) and started to hear some weird noises, like when the radio doesn't have that right frequency it should have and is catching that 'white' noise. Then I started to tune into something but it was like too many sounds, voices at once. I stopped because I really didn't want to get attuned to some weird universe or 'aliens' and it almost sounded like it.
Then I decided I could try to levitate (you know, some yogis in India in deep meditation can levitate, right? I have never doubted that). Not really aware that I was actually separated from the body, I wanted to lift my body, but what I lifted was just my energy legs and that was new, quite shocking and it felt very weird. Not really familiar with it I just played with that state. (Now I am thinking: Would I be really less shocked if the whole my body lifted instead? I don't think so. But I believe everything is possible, the mind is powerful. There are no borders.) I felt that my legs were lifted and were rising. It was exhilarating at first. It felt like my one body was lifting, but my second body wasn't moving at all. It was so strange unusual feeling/seeing. But my head and shoulders stayed on the pillow in my real body. At some point my legs were over my head like in the headstand and I felt the movement of energy like some underwater movement in me. With my legs I sort of made 360' circle probably because my energy head was still fixed to/in my head and I still kept lifting my legs. It was fascinating and it was extra scary and unnatural, too, especially because my energy legs went not only through the wall behind my head (wow) but also through the bed and floor (which I totally wasn't expecting or planning) before I plunged back into my body. Then I straightaway got back to "reality". I was totally awake, including my body and scared of myself. Also mesmerized, but mainly scared. It was all happening at night and I dislike darkness. Who am I? What do I do? What's wrong with me? Is something wrong with my brain? Was it an illusion? What I felt seemed to be terribly real.
Those who went through something similar for the first time, but they knew what they were doing or attempting to do will just smile but there was no one who would understand me or tell me what just happened. A few times when describing someone like my energy legs went through the wall behind my head everyone kept distance and thought I am a total freak. Seriously, I am very glad that there is so many of us who know what it is like, what it is and who can understand. But it still doesn't make me to feel very normal when saying this to someone who never had similar experience.
Now I know it is quite ordinary because I've read about proper astral traveling. Anyway, I have never moved outside the room while consciously having OBE because I had only opened the gate and that was when what I perceived like bad, started to happen and I started to refuse it. So I never went into that state deliberately again.
There is the good and the bad and it all depends on your thoughts, which I hadn't read anywhere at that time but I had to painfully realize it myself. I was about 18 or 19 and in my country wasn't such selection of books on this topic. Not to mention the astral traveling! Because I apprehended that there the thought is the action and my thoughts in that time were mainly sad or depressive, I knew I shouldn't go there. I wasn't clearly ready, I didn't want it again. But it was happening, regardless I wanted it or not. That's why I started to read about NDE and OBE (Dr. Raymond Moody, Dr. Elisabeth Kubler-Ross) but not because I wanted to experience it but mainly because I didn't want it to be happening to me and I wanted to stop it. Now I know it is much better to know and be prepared because when you learn everything yourself with the method try and fail it can be disastrous and very discouraging.
My involuntary OBEs happened mainly during the night and I was getting there unconsciously through the sleep - lucid dreams in the different strength or depth. I could feel it like a plunge into the deep water, into the buzzing energy which was like interwoven with the other much slower and almost hypnotic waves and that always woke my mind up. This caused I felt very awake and scared, because I didn't attempt to have it consciously. The waves were getting stronger and more hypnotic over the years. It was really difficult to get immune against them and not to 'get astral'.
Oftentimes I was also sleep paralysed and I could not get my body to wake up. I was getting crazy, afraid I will just stay there. But the more afraid I was the faster I was getting somewhere else, yeah, the power of mind in an un-mastered action, working against me. There appeared to be the grey heavy energies dragging me down into the darkness and that was petrifying. A few times I somehow just came back and "woke-up" but it was getting worse and worse. Then once I thought of help, it was a few years ago here in UK, I held image of fairies and I started to go up into the lighter 'environment'. I was surprised that my very first saving thought were the fairies, but I live in the town where those little figures of forest, woodland creatures - fairies are in many shops and I perceive them as good.
But since then I have always been consciously thinking of angels, light, prayer and singing when I feel endangered. I've intuitively realized that this helps. I think there you need something good you need to hold on to, something which changes your energy, vibrations and lifts you up otherwise you can just lose yourself. I can't explain why.
I think there are many people who know an astounding amount of information about OBE and astral traveling and have been very successful or some less successful to experience OBE. Some know everything they can know and are desperately trying to enter those states. And then there are the others, usually scared and shocked people who might question their sanity, people who are getting involuntarily just glimpses of some energy body during the lucid dream states, aware of being in a dream phase, feeling threatened by their dreams and also suddenly and without preparation realizing that there indeed is some astral body (theirs) fused with their normal body. In that moment they can even feel attacked, sense the things, here the voices from some other place, dimensions, from beyond. People entering those states spontaneously seem to be the most scared and confused ones, because they didn't wish to go through similar experience. They didn't plan any OBE. It just happened. And they mainly don't know what's happening or what to expect or think.
I don't really know much about it, compared to others much more experienced here (AnneV.), but according to my own personal experiences, I'd think that the voluntary lucid dream state is more like an entering altered state for the conscious OBE and involuntary lucid dream state (when the dreamer is awake, aware of being dreaming, but it happens during the sleep), can sometimes suddenly swap or shift the frequency/level and let the unprepared "dreamer" know also about his energy body, which hardly ever happens during the normal dream states. Some people who don't even believe in aura or chakras and other energy things can feel really bewildered by the fact that they really are the energy bodies. I do sense energies, I can see them all around if I don't want to, different density or light, but I was perplexed, too.
I think many scientists would not agree at all (especially my "farfetched" fairies vision would be tearing them apart), because for them it is all about the brain waves and chemical changes, mental disorders and they mostly don't accept OBE as a fact (as I have noticed on a few websites lately) but as some mysterious ill something they can observe through the machines as the different brainwaves pattern. But they are just observing the manifestation of it in the physical world not what is happening in the energy world. So there will always be some gaps unless they will figure out how to observe it by the other more energy-friendly means. But who of us needs statistics and tables, right?
I can hardly describe what I feel in just a few sentences so I apologize for the length.
Love and blessings
PS I saved my story on my computer before I was able to post it and meanwhile I read about the astral projection on astralvoyage.com. What made me smile was an example of one guy who had similar experience with the astral head still in his head and staring into the headboard of the bed while stuck in the headstand position. Yeah, we are all getting there somehow:)