I have dreams in which I am reading something which I seem to understand, at least as far as the general drift of the text, but when I try to pick out the details, I see that the words and letters taken one at a time make no sense whatsoever. That tells me that I'm dreaming, but it felt so real up to that point!
That's a kind of semi-conscious dreaming, where you know you are dreaming because of the clash of events and dream-facts that do not correspond with facts that you know from conscious memory.
I remember one dream in which a rank of people from work were marching down the street, and in my dream I thought 'wow, this is weird, wtf are we marching down the street for?' Then the dream shifted a bit, but soon afterwards the same bunch of us were 'actually' doing what I had dreamed we were doing, and I thought to myself, 'wow, this is really weird! This is just like in the dream I had a while ago, now it's really happening!'
There are many wakings in which I linger in semi-consciousness, half dreaming, half awake, able to relish the weirdness of a dream, knowing I'm dreaming, but half believing it's 'really' happening. I have the feeling I can slip back into the dream, because I'm curious what's going to happen next. I love that mental state.
Some nights I sleep with classical music playing low on my FM radio. When I'm in deep sleep I hear nothing, but when I start to come out of deep sleep the first part of my brain that wakes up is the auditory mechanism. I hear the music with absolutely acute perception and appreciation, because the rest of my brain is still out of it, therefore I have no distraction. I don't know who I am, where I am, don't know anything but how exquisite this music is. I get that once or twice a year, and it's a thrill every time.
I had a lady friend once bitch about how she went to the ballet with a date, and he fell asleep, so what an asshole he was. This was when I was a management slave, chronically sleep deprived. I told her I fell asleep at musical performances a lot, and I found it was a way to enhance my enjoyment all the more, not tune it out but tune it up, so she shouldn't be so hard on the guy.
I've never done LSD or mushrooms or whatever, but I'm curious about altered mental states. I wouldn't mind tripping out, as long as I had a reliable guide to keep me from stupid stuff. I guess I should count a couple times coming out of surgical anesthesia, but the transitions were pretty rapid, too fast to enjoy. I've read old stories about ether dreams, which sounded pretty groovy.
I remember one episode driving down the highway in my chronic sleep-deprivation days. Any time I was on a long drive, I would nod at the wheel. Lucky I never killed anybody. But one day I went into a fuzzy zone in which I was convinced that I could understand any language with perfect clarity. It didn't last long, and I recognized when I snapped out of it, but I really wanted to go back there.