Do you think this could cause brain damage, and what kind?

well.. you are no longer poor. If it's killing you inside, please just go and have yourself checked. Being young, you got away with doing something really stupid. Personally, I cant say that you suffered long term brain injury. In fact, I'm pretty sure no one here can make such a claim as we have neither the diagnostic examination required to make such a claim, nor do any of us have medical degrees that would give us the license to interpret the results. Just go see a neurologist.