What should I do? Mental Health

Im 15 years old and im mental. I have this urge to kill people, and i feel that the next person that gets me really angry, i will probably kill them. I have dreams where im a murderer and i cut people up and eat them, and for some sick reason i like this. I have a depression problem and i have tried to kill myself about 6 times. nobody knows about it, just me. the scary thing is that this is true, and every time i watch horror movies where people kill other people i get the urge to do this. I know this is horrible, i want to fix it, i just dont know how. My dad said that if i was mental,(just a coinsadence) i may as well drown myself, so i dont really want to tell my parents, please help.