The same as get your shit together. Basically means calm down, don't panic, or focus. Usually said if you are normally good at something, but aren't able to do it well because your mind is preoccupied with something else, or you're just tired.
Kevin: Get your head on straight Amit, my grandmother could have gotten that rebound.
Amit: Sorry man, I'm still tired from that party last night.
While our lifespan is the number of years we will live, our healthspan is the number of healthy years we will have and our sexspan is is the number of years we will continue to be healthy enough to continue having an active sex life.
A lighthearted reaction upon receiving disappointing news of some sort. Usually something that isn't a particularly a big deal, esp. when it primarily affects someone else - sort of a mild schadenfreude. Sometimes doubled or tripled, and possibly said in a sing-songy voice for added comedic effect to imitate a muted trumpet, which is how the meme originated.