Random black outs when angry get violent?

So i have a habit of blacking out when angry but not like a bid mad like im about throw punches.. what could it be...? First time i noticed this was when a friend of mind got smacked across the face by her ex.(well bf at the time) and sorry but im the body guard of my group and well anyone else i think needs help.. but as i soon i saw her get smacked and drop to the ground holding her face while being called whore i felt my blood boil After that i remember rushing at him then nothing when i came to i was i top of him throwing punches and we were both a bloody mess. The second time it was a nother fight (actually they are all fights) but any ways i was in a nother fight and again i blacked out fighting some guy who was picking on a friend of mind for being gay well this time when i came too i was choking this guy and my friends were tryen to pull me off.. I do have anger issues but only when its somethingin volingg love ones or something i cant stand... now i have had my blood boil once or twice and begin to feel like light head and almost black out but i made it stop but im just wondering why do i blackout but my body continues to fight for me and how can i help it? cause i dont like blacking out and i dont like being watched by my friends like a pet every time i get angry they keep watching me like they think ima just snap is it normal or is there something wrong with me..and why do i get so violent i mean i will fight but not till im bloody or he is choking to death please help