Good. 90% of the time you have a bad trip, it's because you've got some sub-conscience thing going on..and you've actually done (whichever) drugs for the wrong reasons.
There are however, times when you may just find yourself in a dark room, sitting on the toilet...and you may feel that the high is becoming to intense. This can often result in a bad trip because you become paranoid about wether you'll ever return to normal or not.

Rest assured, you probably will. This is why i say it's good to have someone around when you're going on a trip...

Duration is not a garuntee'd thing either. it depends on factors. I've found some LSD highs to last only as long as 6 hours.. while others.. i was feeling it the next day.

http://www.erowid.org/experiences/subs/exp_LSD.shtml