The sympathetic nerves are dominant when the body is awake, but when the body is sleepy or asleep, the parasympathetic excitability is enhanced. However, not all people will have an erection when they are sleepy and sleepy. This phenomenon is mainly due to the fact that the body may have recently been tired or sensitive to sexual psychological stimulation, such as excessive exposure to sexually stimulating videos and other books or publications during the day, which can lead to an erection during sleepy and sleepy times. If the erection is only an occasional phenomenon, there is no need to worry about it, you can urinate in time, because the presence of urine in the bladder will also help men to have an erection. If you often have an erection during sleep or sleepy time, and the erection lasts for a long time and does not weaken on its own, it is recommended to go to the hospital for a checkup to prevent abnormal penile erection diseases.