Yahoo'd/Wiki'd: "sudden onset psych disorder" "pysch disorder caused by brain trauma" "bipolar disorder" "dissociative fugue" "Multiple personality disorder" "traumatic brain injury" "Phineas Gage" "preexisting psych disorder worsened by brain injury"
I have a early-mid twenties character who I need to suddenly become insane after he gets kicked in the head by a horse. Ideally, disregarding all laws of reality, I would like him to instantly go from "normal" to River Tam and/or having MPD as a result of getting kicked in the head, but considering none* of my research so far is pointing in that direction, I'd settle for him having a pre-existing psych disorder that no one notices because symptoms are mild (until he gets kicked in the head and they suddenly get worse? is that possible?) and/or no one knows what they're looking at because of the time period.
*- I did find some useful information on traumatic brain injuries, but I'm afraid of mixing and matching symptoms and ending up with a cliche, unrealistic nestful of symptoms. Also, I'd like to avoid any physical symptoms (ringing ears, constant pain, etc) if possible. ETA: By "physical symptoms" I mean, "long-term physical symptoms." Dizziness and vomiting is fine, initially, but decreased motor function or constant headaches is not.
I need the disorder/injury/set of conditions to be big enough that he becomes too high maintanance for his fiancee and she leaves him (picture the stereotypical, uncaring, "other woman" pre-heroine of the story), but mild enough that he's still fairly functional/able to follow the heroine around on her bounty hunting ways (i.e. basically, as long as he knows he's human and can somewhat communicate, I'm good). If need be, the kick to his head can be superficial (it just grazed him, instead of hitting him full on). The point of the kick is really only to give everyone something to blame/a focal point for the hero's "loss of normality."
At this point, I'm thinking about going with bipolar disorder, but I'm really open to anything. :) Thanks so much in advance!