Fandom : Harry Potter.
What would be a possible illness/disease that would suddenly pop up, make person seriously suffer for an extended length of time, only to 'go away', and to come back after a considerable amount of time? (Let's say, oh, over ten, twenty years.)
Cancer and variants thereof are a definite option, however, that isn't the way I'm willing to go. Does anyone have any idea? Character in question is a 17 year old boy (and no, it's not Harry Potter himself.) who is from 1986, to be precise.
I'm pretty much scratching my head at this one, really.
Googled: returning illnesses, recurring illnesses. My English vocabulary is severely lacking.