I think it's all about the tone of the parasympathetic nervous system. It is "parasympathetic" that is responsible for the erection. ("sympathetic" - for ejaculation). So, at night, the tone of the parasympathetic nervous system rises ("night is the kingdom of the vagus"), so a man can normally experience several erections during the night that do not interrupt sleep, and "matins" - as a consequence after waking up.
How is it with what? Naked guy in bed. How not to get excited. (It may even be scary to imagine you paw his sexy body at night.)
Morning erection is one of the most important indicators (indicator) of a man's sexual health. It should normally be regular and complete. Lack of morning erection requires finding out the reason for this.
This is a common occurrence, because, first of all, any man experiences erections in his sleep, and this can happen at the very end of sleep; at the same time, something may even be dreamed of not at all erotic content. Often the reason for morning erections is purely mechanical: friction of a member on the bed.
Have you ever watched the computer turn on?
Then you must have noticed that when you turn on the computer tests all its systems : memory, video card ...
So a man, waking up, tests all his systems for performance, including the genitals.
The reason for a morning erection, most often, is the bladder that has filled up overnight. How? Increasing in size, the bladder begins to press on (stimulate) the prostate. Stimulating the prostate in turn causes an erection.
All because of the phases of sleep (fast and slow) during fast (10-15 min.) a person sees dreams, processes in the body accelerate, the temperature rises, the pulse quickens => an erection occurs. It is essentially impossible to control it. At the same time, it does not matter what kind of dream the man saw - erotic or not.
The reason for this may be overflow of the bladder.
Because the level of testosterone in the body rises in the morning. Why does it rise in the morning? This is another question))) probably because in the morning the body is rested and more energy for sex
Morning erection is not associated with sexual arousal, therefore spontaneous and uncontrollable. Scientists have not yet been able to agree among themselves what is its cause, but they have several theories:
Erections occur during REM sleep;
In the morning, the body checks its combat readiness (and this system too);
The man is relaxed and cannot control his body while sleeping;
By the morning, a man's body accumulates the highest testosterone content. It is he who causes an erection.
Besides, a full bladder is not the reason for a morning erection. This theory was popular enough before, but it has already been recognized as a myth.
In the morning, the production of some kind of hormone there is at its peak (I don’t remember exactly which one), which is why the "hard" occurs.
By the way, due to the production of this hormone, it is better to have sex in the morning)
In the course of a healthy night's sleep, the body is rebooted, "errors are reset" (rest) and its self-diagnostics for full life. Therefore, usually people wake up light, cheerful, in good shape. And a morning erection means that everything is in order with the body.