I was wondering about this. To what extent have you undergone altered states of perception that were not due to the intake of a psychoactive substance? What were the conditions associated with it?
Here's mine:
Fever-induced hallucinations: This has happened to me at least three times in my childhood. The most profound was when I was 7 or so and in my parents' bed. First, I got uncomfortable tactile sensations; it was as if someone was pressing something like half a deck of playing cards or the dull side of a knife into my hands and arms. This then progressed to a sense of both being out of my body and distortions in distance: the ceiling seemed inches away while my feet looked tiny in the distance. Then I began to have a delusion that I was somehow in the wires of a city's electrical supply--I had become an electron. When I tried to explain to my folks what was happening, they got alarmed and called the hospital, which I observed in a very detatched way. I slowly recovered and did not have to be treated. This phenomenon last happened (in a much milder way) when I was ill with pneumonia at 14 or so, and I do not expect to experience it anymore--it seems linked with childhood.
Hypnogogic paralysis pt 1 and 2 I had read how the body paralyzes itself during REM (dream) sleep so as not to act out its dreams. If abruptly wakened from REM sleep, this paralysis can persist breifly; in medieval times, it was commonly referred to as an incubus or succubus--an evil male or female (respectively) demon that pinned you down and often raped you.
My first experience with this was, while sleeping alone, a precariously placed tool box shfited and fell onto the floor. I awoke convinced the house had been broken into, yet unable to move. As it was happeneing, I was convinced I was paralyzed with fear, but upon waking the next day, realized REM paralysis for what it was. I was probably 24 at the time.
A much more sinister thing happened when I was about 34. I was having trouble falling asleep. I was tired but do not believe I was dreaming--if it was a dream, I had a fully accurate image of my room with myself in it, exactly as if I was awake. Suddenly, I felt as if I were being pulled down through my bed. It was very obvoius that this was a highly malevolent force--if you choose to characterize this as "Satan after my soul," I wouldn't quibble. I fought mightily to resist and was ultimately let go. Unlike the first time, upon waking, I had trouble writing this off as mere paralysis, though I could recognize a few features. I'm still not entirely convinced the spiritual aspects weren't legitimate. EDIT: what really made this mess with my mind was, at the time, I was having serious medical problems (since lessened in intensity) that didn't make me suicidal or anything, but caused me to have the attitude of "if I don't wake up, that's just fine with me." Therefore, it made the demonic aspect to it much more believable, though the rational explanation would still be hypnogogic paralysis.
Exertional euphoria: I'm sure most are familiar with endorphins, of which I've had experience. Twice though--both times after extended exercise, once hiking out of the Grand Canyon--I felt literally high: a combination of lethargy and euphoria. My suspicion is that this was a combination of endorphins and low blood sugar (in the G.C. case, ran out of food on the ascent and the last 3:30 or so was without carb supplementation).
There are a few things I haven't mentioned, such as deliberatly getting dizzy or hyperventilating as a youth, or meditation (it took a lot of effort to truly acheive an altered state this way and actually was unpleasant once reached.) So much is written here about specific effects of specific substances; I was wondering if anyone else has had similar "highs" without a single ingested chemical.
Word! I have had off and on this Hypnogogic paralysis since I was 15ish and as early as last year had this experience. I dumbed it down to my mind waking up before my body and was satisfied with that but now have a name for this shit. The first time it scared the ever lasting shit out of me. I could not sleep the rest of the night because of my lack of understanding of what the fuck happened. One of the first few times I remember trying to scream but could not. It feels like ones a quaddriplegic but you just wake the fuck up to it, no transition. A couple years ago I was not as frightened when it happened and became somewhat familiar with this and a few times thought in this state I could leave my body and do some astral projection yet never suceded.
Another thing I can identify with is your image of the room. Every time this has happened my eyes were open which is where the fear came from.