Why do you get a hard on in the morning?

What is too skinny for a 12 year old who is 4'11? Define community health? What is a good blood sugar in the morning when you wake up? Do the doctors need to give you medicine after stepping on a nail? How often should you change your pantiliner? Who deserves respect? Is it normal to weight 56kg for a 16year old girl who's 171cm tall? What does it mean when you have a booger that's yellow-orange? What does a specific gravity of 1.030 mean? Which structure is in close relation to ligamentum arteriosum? Why do girls not like Asian American guys? Who now manufactures a Fisons Pharmaceutical Division ointment called zambuk and where can it be obtained? Does mercury accumulate in your body once it is being consumed? Why do girls bite their lips when talking to boys? Do people die from Polymyositis? Why Fred hollows is famous? How long does it take for bleach to disinfect most surfaces? What if you have feelings for your current boyfriend as a friend but may still love your ex? Is it safe to go in a hot tub with too much chlorine? How can you tell if your crush likes this one girl that he's known for years and he jokes and laughs with her does he like her or is it just because he's known her for a while?