Brain dmg, personality change

The strongest evidence supporting brain -> consciousness is that. But i was just thinking, im normally a modest person, but after hangovers i feel like shit and temporarily get aggressive and lacking sympathy. To an outsider thats a personality change, but i know its due to frustration/agitation/general discomfort that makes me act like that.

You always hear about people's personality change after a life event, e.g. divorce/losing kids/bankrupt etc. In those cases its also because of the psychological pain that cause a change, and the frustration/lack of satisfaction they feel on a constant basis. The person's personality hasn't truly changed obviously.

Might people with brain dmg be experiencing a "constant agitation" that cause them to become immoral and impulsive? E.g. phineas Gage. To an outsider, its not really clear whats causing a person's change, because if brain damage gives the person a constant discomfort, or removes certain cognitive functions (which in effect creates a lot of frustration), it'll dramatically change their personality as viewed by an outsider. Has there been any research done into this?