When does it happen? While asleep, our bodies enter a period known as REM, or rapid eye movement. This period can last from a few minutes to a half an hour and is the point in which sleepers have the most vivid dreams. Wet dreams, or nocturnal emissions, usually occur during the REM period of sleep.
How often does it happen? There's no average number--some can have wet dreams once every two months, or more rarely, once every two days. There are some people who have never had a nocturnal emission at all. One interesting thing to note is that a person who sleeps in is more likely to have a wet dream than someone who wakes up early because the extra hours lead to more REM sleep. So, based on this, wet dreams are more likely to happen on the weekend than during the typical school week.
