What I would like to know has anyone experienced or know of similar experiences with welding machines exhibiting such a detrimental behavior. After any injury with a machine, the machine should be locked out until it has been checked out and the situation rectified. Electrical shocks happen in welding when the person becomes a better ground than the ground cable. The machine must be grounded as well as having a electrode cable and a ground cable. Obviously, standing in a bucket of water with your feet soaked makes you a better ground.
Some machines are water cooled - make sure there are no leaks.
Because you mention that this is a TIG welder - there are certain concerns with TIG welding. The cycles involve the electrons going one direction and then turning around and going the opposite direction. There are 60 complete cycles per second. So, most machines used for TIG welding are equipt with a high-frequency switch. The cycles vary with the machine, but most that I have used are 100,000 cycles per second on high frequency.