It is an old Eastern philosophy that ejaculating drains the male body of its “life force,” bringing down its testosterone levels. This “life force” gives men energy, and testosterone gives them more aggression. The myth pertains to logic, but the reason you feel sleepy after ejaculation is because of the chemicals that are triggered during the ejaculation process are sleep inducing. Regarding the lowered testosterone levels; scientific studies have found that having sex actually increases testosterone levels. In fact, three months of abstaining makes a man’s testosterone levels drop to that of a child’s, which does not bode well for the increased aggressing or energy necessary for the edge in some sports. Overall, if you want to do it, go for it. If you find it affects your performance, just don’t do it the next time.