Here's an idea, and it may be something that already exists I'm not sure (please do comment if you are aware of anything similar to this) tieing hypnosis with fantasy.

I know there already some hypnotic stories and such around which are meant to make you experience a fantasy based narrative. But could you hypnotise subjects to be triggered by something like a full moon for example, making the subject feel more powerful, or hungry, kind of like turning them into a werewolf. Alternatively you could have triggers to sunlight, the feeling of nothingness when you stare at your own reflection, and such to simulate becoming a vampire.

Anyway these were just some fun ideas I thought of. Happy to get others throughts on it.