I had noticeable psychosis courtesy of ketamine in the ICU after being run over by a truck. Likely having a broken pelvis etc. didn't contribute to a positive trip, of course, but I would be very reluctant to take it again (not that anyone asked at the time - or that I could have answered sensibly). But like most psychoactives, dosage is key...
The WHO lists ketamine as a "essential medication" since it is an ideal anesthetic for countries with limited resources. It's quite safe (doesn't depress breathing) and effective.
However, as you noticed, many folks who are treated with ketamine find the experience very unpleasant. Unless there is a good reason for using it as an anesthetic, doctors typically go with other drugs.
