I have the same problem..So I asked my instructor once he admited that he get the same thing in real life fighting. And said this is completely normal as long as it doesnt affect ur thinking. this is your
adrenaline kicking in, and is perfectly natural !! infact the
adreanaline well help you to defend your self.
Read this you will now wot i mean
http://www.nononsenseselfdefense.com/fear.htm
The gift of fear is nice book