I don't recall any concussions or injuries to my head. At least nothing major or memorable. Crossing my fingers, I have to say that I've never really had a serious physical injury in my life.

I googled this topic, out of curiosity, and there are results from reputable sources. I would wonder if it is really the concussion itself that may or may not cause mania (or other mental health issues) or if it is the stress resulting from the injury that may or may not cause such issues? I have definitely read many many times that a major stress (or trauma) in life can trigger the disorder. I do know that I had a major stress trigger at 14 years old, when I am sure my first bipolar symptoms started to show. But that was a psychological stressor/trauma, not a physical injury. I clearly had episodes from that point on, but my worst episodic periods were linked to serious psychological stressors or traumas.

I have read that people who develop bipolar disorder generally have a genetic predisposition to it. What I read stated that there may or may not need to be a trigger for the start of the disorder, but often there is. I read that if there isn't/wasn't, it could be possible that a person avoids the disorder (if lucky), or at least major symptoms of the disorder, by it remaining dormant. This is just one theory, but a popular one, I believe.

About a week back, I created a thread asking people to share their mental illness treatment histories. In most all cases, the history started with some kind of stressor of sorts. I saw many of the histories begin in adolescence, which I see as a stressful period. Others were more in their college years. Again often stressful, in a way. Then there is post-partum in many cases (like my paternal grandmother). Again stressful. Or other major life events. I don't think it has to be a very major stressor, though.