The Ancient Greeks saw a man's daily “sunrise salute” as evidence that “the penis possessed his own will”. Medieval monks, on the other hand, saw it as a sinful rebellion of the male’s body. So, what does science have to say about the story of morning glory?
Scientists call it nocturnal penile tumescence and it’s been the subject of scientific investigations since the 19th century, just like most matters involving a penis. Despite the glossy magazine myths, a morning rise is not evidence of a sexual dream. In fact, it’s not directly associated with sexual desires at all. Morning penile erections are involuntary and can affect everyone, from babies in the womb to the most prudish monk of the Middle Ages. Equally, women get clitoral erections during sleep too.
During our sleep, we drift through numerous phases of rapid eye movement (REM) sleep and non-REM sleep. In REM sleep, our minds dream and our nervous system undergoes a shift in balance from sympathetic nerve activity (which stimulates “fight or flight” responses) to parasympathetic nerve activity (associated with the “resting and digesting” or "feeding and breeding".)
This shift towards the parasympathetic nervous system results in your brain shutting down some of its chemical messengers, one of which is norepinephrine, a neurotransmitter that constricts blood vessels and helps to restrict blood flow. Without as much norepinephrine pumping around your body, blood flow commences and a hardon will arise.
The result is three to five erections during a full night's sleep, with each erection lasting around 30 minutes. Humans can wake up during REM sleep, so it’s perhaps no surprise that you wake up with a morning horn.
This still raises the question: Does it serve a purpose or is it some strange glitch of the nervous system? Well, scientists are not totally certain. However, there’s some evidence to suggest it could help your penis stay nice and healthy. One of the main missions of the blood is to deliver it to tissues. Lots of blood flow equals lots of oxygenation, meaning the tissue is healthy, prepped and ready to repair itself, and go about its daily business.
So, next time you wake up "pitching a tent with no camping equipment", it's just your penis looking out for you.