Night fall is a desease.isnt it?and if it is not then what is the normal occurance for a normal man in a week?

Not a disease: I've learned from this website that "nightfall" is a term used in india for nocturnal emissions or "wet dreams." this is not a disease; it's a perfectly normal occurrence, especially in adolescent boys and young men. The frequency depends in how often you ejaculate through sex or masturbation. If this bothers you, masturbating before bedtime will make it less likely to occur.

It is not: You're a man now and you need to learn about your body. I'm very sorry that somebody has deceived you into thinking that nocturnal emissions are unnatural or unhealthy. If you don't make yourself ejaculate during the day by yourself or with a partner, this will happen. It varies greatly from man to man, and can be nightly or several weeks apart. Talk with a wise older man -- maybe even Dad.