The erection occurs 3 or more times during the night during REM (rapid eye movement) dreaming sleep. During this time there is more blood flow to urethra which causes the erection.
Here is A LOT of different answers i found in another question here.
More answers down below
Morning erections are technically nighttime erections which happen during Rapid Eye Movement (REM) sleep (when most dreaming occurs), although men older than sixty years may have them during even non-REM sleep. Generally, we experience four intervals of REM sleep per night. These spontaneous woodies in the wee hours are caused by specific neuroreflexes (whatever the word is called.) that are stimulated during REM sleep.
An erection has been proven to greatly relieve the pain of needing to urinate badly. The reason is because when you get an erection, a valve stops the urine from entering the urethra so that only semen can pass through the urethra during ejaculation. So the next time you're in your car in a traffic jam and you REALLY need to go... just use your imagination. Ha ha It works every time. It is partially why you have morning erections since it helps prevent you from peeing on yourself! Ever notice how difficult it is to urinate with an erection? Ever peed on yourself in bed since you hit puberty?
TRIVIA NOTE: the proper term for this phenomenon is Nocturnal Penile Tumescence!
it might be due to the dream you have been having that was perhaps about your girlfriend with no clothes on.
An alternative reasonThe reason a man gets an erection in the mornings is one way to see if he is sterile, I went to the doctors with my wife to find out and that was one of the questions on the form I was given and they told me that it is a 98% chance that I am not sterile. and I thank god for that, but it is also a build up of testosterone in the male, more than likely though you will not have it if you have had a vasectomies.
Morning erections in men, also known as nocturnal penile tumescence, are caused by a combination of hormonal changes during sleep and increased blood flow to the penis. These erections are a normal physiological response and are not necessarily related to sexual arousal.
Not in standard urination. However, after erections, men often need to urinate, this is a biological function designed to "keep the pipes clean" and free of organic materials.
Morning erections, also known as nocturnal penile tumescence, are caused by a combination of hormonal changes, increased blood flow to the penis during sleep, and the relaxation of certain muscles in the body. These erections are a normal and healthy physiological response that often occur during the REM stage of sleep.
No, women do not have the anatomical structures necessary to experience erections like men do.
often excitement.
No, it is common in most men who get random erections (erections that occur when there is no sexual physical or mental stimulation) or men who have prolonged sex with no ejaculation.
No, women do not have erections in the same way that men do. Erections in men are caused by increased blood flow to the penis, leading to its enlargement and firmness. Women do not have the same anatomical structures that allow for this type of response.
Yes, men can give themselves erections through physical or mental stimulation. This can include touching, fantasizing, or other forms of arousal that can lead to increased blood flow to the genital area, resulting in an erection.
Some do some dont
They can do yes. These are called spontaneous erections or involuntary erections. They occur when blood suddenly rushes into the penis (erections are caused by blood flow into the penis). It's very common in men when they wake up in the mornings.
No, women do not have erections like men do. Erections in men are caused by increased blood flow to the penis, which is triggered by sexual arousal. Women experience increased blood flow to the clitoris and vaginal area during arousal, but this does not result in a visible erection like in men.
Men get boners (or more correctly erections) when they usually see women or if they are gay another man. Women can discharge if they are sexually aroused by looking at a man. During puberty erections may come at unusual times. Mature men generally only get erections when they are sexually aroused. If a man is homosexual, this arousal will be triggered by other men. It's possible that you, on some level, find other men to be sexually attractive. It's also possible that while you were gazing at a man, your mind was thinking about something sexual, whether related to men or women.