Maybe i was lucky that I didn't try shrooms on a party but on my own. Maybe a bit risky, but i have no mental or childhood unresolved issues, and I am fairly well balanced person with rich inner life (yeah, introvert).
What I experienced - the journey inside of me and back, lost of connection with all physical aspects of existence, including all senses (which is funny, because you 'see' amazing things with your whole entity, but when coming back down and slowly plugging back eyes you realize how limited and 'different' they are compared to what you just experienced, same goes for all senses but eyes are most obvious).
I could go on and on for hours how profound the experience is, it's truly some sort of 'higher' state of mind compared to daily existence, but since much more of hte brain is engaged (or with more intensity, dunno), after few hours I am extremely tired mentally, and usually strong migraine comes (that goes away over night). The breakdown of oneself into endlessly small atoms, dance of them in endless whirl of time and space, and slow reconnection bit by bit when the trip fades away (which takes at least an hour or two and is as interesting as going up). After first time experiencing it, I knew I don't have any predisposition for mental disorder, since this breakdown into flawless mist and back would reveal some inconsistencies in my persona. Or the sense of breathing - registering it, but as something very distant, not really that important, pausing it for minutes (or at least it felt like that).
Anyway, for me to get there, I always have to lie down, ideally in comfy bed, with nice quiet shamanic music in the background, curl under the blanket and cut all feed from all the senses. Other people and stimulis would be just interrupting this journey. Party would go in exact opposite direction. I also mixed shrooms with lemon juice - gives it maybe 5x intensity for given amount, and trip lasts maybe 3 hours which is plenty for life-changing experience).
Coming down is experience itself - the sense of endless inner peace and true happiness that brings smile on your face as reflection of state inside your mind, and landing back is very smooth.
It's so strong I never done it more than 1-2x per year (availability is also an issue). Didn't do it for last 5-6 years at all, but the effect will be with me forever. I don't believe in some higher forces or magical wonderland and whatnot, just that our brain can provide us with truly breathtaking experience once we alter the way it's engaged. Did try Salvia divinorum extract few times - similar effect I would say, much shorter and shallower, but same type of setting, cutting of senses and coming back scenario.