Hello Offcourse nightfall is natural and not a disease and occurs with almost everyone though the frequency varies. Its not due to overflow of semen infact there is nothing like overflow or decreased store of semen due to loss. Masturbation isnot the misuse of private parts and doesn't lead to nightfall, infact regular masturbation can decrease the frequency of nightfall. Actually its the deeply ingrained myths often propagated by quacks which make us resistant to accept sexuality as it is.