Masturbation is a sexual stimulation of genitals (most often one’s own) to the point of orgasm. Although in history masturbation was related to various health problems (mental problems for example), today there is no evidence of such relation. Masturbation is considered a normal, completely healthy habit through which a person relieves its sexual tension. Excessive masturbation in male might lead to temporary inflammation of the penile mucosa due to increased rubbing. This is more likely to happen if the male rubs himself against surface instead using his hands.
By not releasing the semen regularly, the male might feel great sexual tension and in some male pain might be felt in the testicles. This might be due to spontaneous, uncontrolled erection during sleeping when the testicles and other tissue in the area are more supplied with blood than usual which might cause small edema and pain. This condition is temporary and once the sexual tension is decreased the symptoms are usually gone if there is no infection present.
You might want to talk to your family doctor or to urologist on this issue.