I don't know about it increasing ticklishness, but it is possible and real, I've seen it done live (without tickling, though). From my understanding, you hypnotize the person and then tell them where they'll feel tickling whenever you say or do a certain thing. Maybe like when you say a certain word or snap your fingers. Also, to my understanding, when they "wake up" from being hypnotized they won't actually remember anything... It's like a dream, they may remember parts of it, but most likely not the whole thing.