By Kayla Kibbe It’s Valentine’s Day, and you know what that means: sex. For many men, it also means falling asleep almost immediately afterwards. It’s a bit of a tired cliché at this point: man ejaculates, rolls over and passes out, leaving his disgruntled (and probably sexually unsatisfied) partner awake and annoyed. While this is one of the many lame, heteronormative sex tropes perpetuated by sitcoms of yore that may or may not have destroyed countless millennial marriages, it turns out there is some truth to it. If you find yourself feeling sleepy after sex, it’s not just because you’re a s…