There are a few things you can start of with:
– Make use of those things that are calming for you
– Try and refrain from staying in places or conditions that make you angry
– Move from those circumstances when you feel the anger coming
If it is unintentional due to your health condition as you said then don't press over the issue that it is a sin because that will make your mental health situation worse. Do istighfar for the mistake but don't keep on pressing on the matter of it being a sin.
Such thoughts will worsen the situation. Continuously try and calm yourself and ask Allah for help.