** Thanks for contacting with your health concern 1. with men sexual response occurs when there is some form of sexual stimulation, like touch, smell, thoughts/fantasy [present in history] and it is impossible to separate physical part of sex from thoughts, feelings, and reactions. 2. since with stimulation/arousal there is definitely increased blood flow to the penis resulting in penis getting larger and harder thus divert the mind to non-sexual activities like sports or business matters. PS. Since it is very difficult to remove misconceptions from the mind you can consult a psychiatric who may prescribe placebo treatment, e.g . mild tranquilizer at bedtime 3. Masturbation is not related to size of penis, main reason is guilt and is more of a psychological problem than Physical and remember masturbation will not cause fatigue, sexual illness or reduced function, health issues or low sperm count, in fact, it is a natural phenomenon of body to relieve itself of sexual urges. PS. Over masturbation becomes harmful only when it becomes a Disorder