The autonomic nervous system controls the body's involuntary muscles, including the digestive tract, heart, and bladder muscles. It also regulates your body's temperature control, making you sweat to cool off and shiver to warm up.

During urination, the autonomic system can get overstimulated. "In addition to the messages the system is sending to your bladder, it may also communicate with other areas," Hence the shiver.

This phenomenon can be a real health problem for some men: They can pass out at the urinal when their autonomic system cues a drop in blood pressure!