Healthy 19 yo. Bent over to pick up a toy got a sharp throbbing pain in back of head. Stood up and it slowly went away. Worried? Aneurysm?

See below. Problems like these can only be correctly handled by your doctor in person. He/she needs to listen to you, perform an examination and possibly run labs or other tests. That's the only way he/she can find out what's going on and what to do about it.