Personally, I never look to abort a trip. Often times, the most profound insights occur during trips which have turned sour, and I usually end up feeling stronger after its over. Sure, things can get pretty scary, but I kinda feel that if you're not able to "deal with yourself" and ride out the waves of terror and anxiety through meditation, you shouldn't be doing so many drugs. It's like, you bought the ticket, so take the ride...if you hop off early, you don't reach your destination, and the trip was pointless. Psychedelics should be viewed with more respect than simply a means to get fucked up.