A few years ago, I spent about 3 days at 12,000ft (slept at 4,000 & woke up and hiked to 12k for the remainder of the trip). I came home, and five days later, I drove from sea level & and dayhiked to 13k. Whilst on the summit, I noticed people acting strangely, stumbling around & carrying strange expressions (vacous) on the faces. I asked a couple of them to take my picture, but they seemed disconnected. I thought "crap, is there nowhere that I can go where I don't run into the nutcases??" It took me to halfway down the mountain to realize that everyone else on the summit had also tried to do a dayhike, and they were all zombied out from degrees of AMS. I lauged out loud, because I totally forgot that altitude bothers people! I do not know what the stats are for how long acclimatization lasts, but for me, I have been extremely lucky.
