I suppoose this could be due to a medical condition that requires treatment, only your doctor can tell. That being said, I will also say I see shooters shake all the time while shooting. Some right from shot one, others after a while. The thing is that each and everyone of them is almost choking the grip to death while trying to maintain good gun control. This usually makes them shoot all over the place and they can ot figure why their groups get worse the harder they hold their handguns. Gripping that hard causes rapid onset of muscle fatigue and you begin to shake. Once I get, or got (as I no longer instruct), them to ease up their grip, the shaking went away and the groups got much better.
Another time you will notice shaking is if you are ever in an armed confrontation. You don' even have to fire your weapon, you will wind up shaking. That is from the let off off of adrenaline.