My dad is suicidal, what do I do

My parents have only been together for the past 6/7 years (my father is a musician and left to travel the world before I was born then when he came back they got back together), things have been great, I couldn't ask for a better family. But there has always been a huge problem because my Father was a self harmer and has bi polar...However he hasn't hurt himself for around 10 years now. Every day all he does is wake up at 6pm, goes into the garage (which he has made into a recording studio) and smoke pot till 9am then goes back to sleep again...This has been his day-to-day life for the past 4 years. Only recently has he actually realised that he cannot carry on living life the way he has been, him and I spoke about this recently and I tried to give him some advice (we have a very good relationship, like best friends) but he's literally just given up, I think this is because that's how lazy smoking pot for the past 30 years has made him. He can't even be bothered to live anymore...He told me he was suicidal, which due to his bi polar I have heard him say before...But this time it was different, I really believed him and he was telling me how he was going to write a letter for myself, little sister and Mum. Two days later I went away for 3 nights, and when I came back he told me that when I was away he had self harmed (something that he has not done for 10 years), this shocked me because now I am very worried for his life and have been spending every minute I can with him to try keep a smile on his face, but due to his sleeping pattern he spends most of the time he is awake alone (which will not be very good for his mental health anyway). I don't know what to do because whenever I mention him getting some professional help he just says that he's had every therapy in the past and it hasn't helped, he's completely given up and I don't know what to do. I've tried talking to my Mother about it but that doesn't help because she has narcissistic personality disorder, so she always finds a way to make the situation about her and that she needs help, which to a certain extent I do understand because it cannot be easy having my Father as a partner.I just don't know what to do anymore, he's always had very bad episodes, but its just the fact that this time he actually did cut himself that I'm worried about...Please help me help him...

How do you know your mother has NPD? Has she been clinically diagnosed? Anyway, I suggest you visit and confide in yours or his GP. How old are you, by the way? Where did he cut himself, and was it deep enough to need stitches?