Totally natural mate.
If you were getting into a normal fight. Your fight or flight instincts would kick in, youd feel all sick, blood rushes to your hands and feet and adrenaline pumps so much boxing gms stink of the stuff.
It is a side effect of the adrenaline, and the fact that your worrying.
I dont worry too much anymore, i feel relaxed, but im a laid back sort of guy so its easier.