Hello, Nightfall is the uncontrolled ejaculation of semen during sleep. This is generally caused by sexual arousal and orgasm from dreams. Night fall or nocturnal emission is completely normal for males during teenage and early adult years.
When boys enter puberty, there occur a lot of hormonal changes. These changes can result in spontaneous erections during sleep or, during the day and nocturnal emissions. These are simply a part of normal development. Nightfall or wet dreams is normal for a teenager, this happens when the body wants to get rid of the excess sperms, the cause for this is that you are not masturbating.