I haven't done this since I was in my early twenties, and my depression was at its absolute worst.
I used to hit myself in the temples with my fists, so hard, over and over again... I'd see lights, and get massive headaches, & feel dizzy. I also used to beat my upper thighs, until my thighs were a mass of black bruising for days.
My trigger was feeling so incredibly angry and enraged....and yet feeling completely and totally helpless to express it or have my concerns taken seriously.
Now I'm more apt to punch my desk or a wall, on the rare occasions I feel that way. I think I've just completely sublimated it somehow.
I don't think anyone in my family knew I was doing that. My current husband does, because we tell each other stuff.