Extreme excitement to rage every half hour or so

I would suggest a brain scan. I think it's a likly brain tumor. Bipolar disorder isnt this fast of switching and swinging. Though a brain tumor on the other hand can cause pressure on the brain causing a multitude of ailments or emotions.

Just a theory with the brain tumor idea. If it is a brain tumor the tumor is causing a rush of anger which in turn increases your heart rate and adrenal glans causing even more damage in the brain due to the swelling of both the brain and tumor. When the anger goes on long enough without a cause the brain automatically releases endorphins to calm you down thus slowing down bloodflow and decreasing pressure. Though I'm not a doctor I would be pretty surprised if my hypothesis was legitimate.