Erection of penis during sleep in NOT normal. I, being a doctor (Homoeopathic), strongly advise you to consult a doctor immediately since you are not having full erection. How many times do you masturbate in a day, if you have the habit of doing it. Some people say that masturbation has ill effects on erection and dysfunction occurs if you practise it. But it is wrong. Of course excessive masturbation may cause erectile dysfunction.
Don't worry.