AFTER SEX EFFECT – REFRACTORY PERIOD

The period after orgasm (known as a refractory period) is often a relaxing experience, attributed to the release of the neurohormones oxytocin and prolactin, as well as endorphins (or “endogenous morphine”)

An increased infusion of the hormone oxytocin during ejaculation is believed to be chiefly responsible for the male refractory period, and the amount by which oxytocin is increased may affect the length of each refractory period.Another chemical which is considered to be responsible for the male refractory period is prolactin, which represses dopamine, which is responsible for sexual arousal.

http://en.wikipedia.org/wiki/Refractory_period_(sex)