firstly, after sex, sperm bank in the balls drun run, so it
definately need some re-generation...so while you resting...it is
making new sperms in the process...
as for the hard on erection, well it's just normal process found on
every normal males...teacher last time did explain to me why this
happens, but i kind of forget the explaination already...sorry for
not being able to answer your query...
