I've tried self-hypnosis for HH but it doesn't really work (every day I'm currently listening to mp3 I bought off of a reputable hypnotherapy website).
I've found that hypnotherapy helped me dramatically for my social anxiety and feeling comfortable around people, but not for the sweating. It's weird, because I don't feel anxious anymore in social situations like I used to before hypnotherapy, but I still sweat too much (I have generalized HH triggered by social anxiety).