Semen production is an ongoing process in male body, whenever body loses semen it reproduce to replenish the lost one. Male body ejaculates semen during sleep to discard old lot when there is not any ejaculation through mating, but in many cases this loss of semen during sleep occurs too frequently. Since male body quickly replenishes the lost semen hence frequent ejaculation strains internal organs responsible for producing it and causes deficiencies of vital nutrients in the body..And its considered normal...