The average man who has no physical impediments to erection has anywhere from three to five erections per night, according to MedlinePlus. This is known as nocturnal penile tumescence. Each of these nighttime erections lasts for up to 30 minutes, and most occur during REM (rapid eye movement) sleep.
Not only are these nighttime erections normal, but they also play a key role in the maintenance of healthy erectile function, sort of like exercise undertaken in advance of the big game.
While most men are totally unaware of most of their nocturnal erections, almost all of them have awakened in the morning from time to time to find they have an erection. According to the U.K.’s National Health Service, this is usually the last of a man’s nighttime erections and is known by some as a “morning glory.”