It is a central nervous system reaction to adrenaline sweet cheeks! very complicated feed back system and that is a very simplified version......I been there many times in a big way, but usually if I am at that point, which doesn't happen very often now, everyone runs a mile!!! It will get easier as you learn to control it babe, the restraint from acting on your anger is what causes the adrenaline surge which makes you "spasm" or shake. Adrenaline wants you to run, defend, fight, hide......once you control the anger, you can control the physiological response to it. Thats why I was put on anti-psychotics and tranquilisers initially, because I could not control my rage......it was like an untamed beast(hence the invention of my "werewolf"!)

Hope that helps........I have done A LOT of reading on anger and physiology.....very interesting topic and overall you can see how dangerous rage can be to your health.......

It will get easier......breathe slowly through it....remove yourself from the stimulus and rub your muscles vigorously but calmly....don't forget to breathe and it will pass......