I've got another story idea I've been playing with, but never got around to using. If anyone is interested, you're free to use it as I'm unlikely to. It concerns a guy who suddenly sees little 'critters' pestering people. Upset at their fury, he attacks them, beating them off. Questioned by the authorities, they suspect mental illness, until the people he 'defended' report that their mental illnesses are gone. The general idea, which gets expanded over time, is that these 'demons' (which look different for each mental illness) actually access our world through dimensional portals to harrass people.
As he helps more people, he tries to figure out what's happening, only to discover he's got an undetected (until then) brain tumor--supporting the fantasy element of his visions--except everyone he helps reports they're cured of lifelong mental illnesses.
It then comes down to, does the guy try to get better, losing his ability to help people, or does he risk an early death to advance a movement that no one believes in. Adding complications, the demons learn to recognize him and begin setting out traps for him.
Feel free to change any aspect of the story you want. I give up all rights to the story since I never wrote anything (i.e. no way to enforce trademark) and I've given up on ever actually writing it. Possible title: The Demons Within.