I had something like this recently, I'm talking two weeks ago... It was the weirdest thing ever, I've experienced many pyschoactives, but it wasn't quite that, I'll explain better. I was very sick, I had a fever, and overall felt like crap, I just thought I wasn't getting enough oxygen, and it was dumb of me to be working anyway. Okay, anyway, I was walking down the hall at work, it came on me suddenly and I felt as if I was going to faint. I felt half awake and half asleep. I felt as if the walls were closing in on me in every direction. Every movement I made was a horribly slow echo. In my sight of vision the walls, ceiling and floor all closed in in a perfect square squeezing out everything in my sight, I leaned against the wall and everything went grey and I had the horrible echo of some sort of something in my head and whole body. I don't know how to explain it, i can recall it quite well though. I didn't really think of it then but it did have some shapes related to it, but not visually, not something that I could define, or see... it was more almost like the vibrations echoing off of my surroundings, and thoughts giving them shape. That's a really odd and vague description, but it's the best I got.