Nightfall or nocturnal emissions is spontaneous ejaculation while sleeping.there is nothing to be ashamed of it as it is occurs in most males and is body's way of getting rid of collected semen.The frequency of nocturnal emissions varies.it may be more in those who are sexually inactive, with no engagement in either intercourse or masturbation, who watch more porns, due to stress. It doesn't need treatment though but you can reduce frequency by lifestyle changes, relaxation exercises, avoid watching porns, don't over worry about nightfalls.And about small penis, many males feel they have small penis when actually they wil have normal size. Reasons for small penis could be genetic or hormonal imbalance(reduced testosterone). Consult sexologist once.