Yeh thats happened to me after clearing 3 bowls consecutively, stood up and felt fine, then everything went a lil bit louder, then a lil bit brighter, then started to go black around the periphery of my vision until it took over everything I could see, and sounds were like if u taped a balloon to both ears. After I slumped on a bed, it slowly came back over the course of 5 mins, and I was off my tree, havin flashbacks of my first shroom trip, u jus pulled a whitey, sumtimes u puke, sumtimes u get all lightheaded, sumtimes u'll str8 pass out (saw a girl I knew do this and crack her head off the wall right in the middle of me talkin to her, rude bitch lol) I got the same thing a few years back aswell off of only 1/2 a spliff, was walking across the road and I couldn't see a fuckin thing, sounds were fuzzy, again it came back within 5 mins, so don't worry yourself, it probly won't happen again for a looooong time, been smokin 5 years and that shit has happened about 3 times to me.