Hi Welcome to HEALTHCARE MAGIC.. I have gone through your query and can understand your concern... Masturbation doesnot cause nightmares. Nightmares are caused by psychological causes such as stress, anxiety,etc. As you are 21 years old your height might not grow now. this is due to fusing of epiphyseal cartilages. This happens to every person. Nightfall is not a disease. When seminal vesicles are full of semen and frequency of masturbation or sex is low, excess semen comes out on its own during sleep which we call night fall. As your frequency of sex will increase nightfall will decrease on its own. Don t worry you would be fine Hope this information helps.