What's wrong with me? Imbalance? Depression? Migraine? Something worse?

Over the past few years I have been noticing some subtle but disturbing changes in my mental function. It first started about 3 or four years ago when I blacked out after a long hot day at marching band camp. We practiced on the parking lot so naturally it was hotter than normal. I thought it was just heat and I brushed it off. It happened a few more times over that year and the next but again I brushed it off. Well I went through some pretty traumatic stuff with a verbally and sexually abusive boyfriend and I was in a car accident in which I broke my nose in two places a little over a year ago. Last summer I went to an amusement park and on one of the roller coasters I felt myself black out. I got light headed, felt myself go limp in the seat and I couldn't see; everything was black even with my eyes open. It really scared me. This past year I have off and on feeling of tunnel vision. Almost like I have blinders on and it feels like there is a large amount of pressure on my head

you need to consult with a neurologist. Multiple diseases have those symptoms. (eg.- migraine, epilepsy) or maybe is only vasovagal syncope. ask for professional help

no idea, i would definitely see a doctor and get a referral to a neurologist. Stop brushing it off!
it could be migraine... you really need to see a doctor and a neurologist... they will advise you to have tests (it could be a virus) and scans
sounds like you have a problem, if i were you id see a doctor. youre most likely to get a better answer than you would on here. good luck.
You need to have a catscan...it sounds like you might have a brain anurism..this can be treated if caught before it gets to bad..but the symtoms sound like it..it could also be your blood sugars are unstable..either from a bad diet or too much sugars...you need to be checked out..really