Post-micturition convulsion syndrome, also known as piss shivers or pee shivers, is a phenomenon where one feels a shiver running down the spine following urination. It is experienced mostly in males.

Although no serious studies have been done in this field, there are a few theories to explain this phenomenon:

Sudden loss of temperature and blood pressure
Stimulation of nerves in the tip of the penis
Parasympathetic nervous reflex (a catch-all explanation for such things).