You are experiencing the symptoms of hyperventilation (look at the central nervous system symptoms – paresthesias mean numbness and tingling). You may also experience tingling around your mouth in addition to your hands and feet. Basically, you are overbreathing, and releasing too much carbon dioxide from your breath (one of the primary functions of breathing is to release carbon dioxide, in addition to inhaling oxygen). When your blood CO2 becomes too low, less blood is delivered to your brain, leading to the major central nervous system effects. Further, the effects of reducing blood CO2 is to raise blood pH, which affects blood and tissue calcium levels (and ionization), which is why you feel the numbness and tingling. If you relax, slow down, and take normal breaths, your body will compensate quickly. Or, you’ll pass out (which is what happens when people hyperventilate), and when passed out, your body will correct itself. Edit: I modified it a bit. Also, don’t pass out in the tub…