I was in a very very similar situation, working as a software engineer on highly important safety critical systems I was at the peek of my career and very successful. But I was working way too hard, not sleeping and drinking more and more booze. It was OK but borderline. Then a couple of issues pushed me over the limit, and the booze intake got higher and higher. It took probably 3 years of gradual decline before I had just about shutdown, work was about to fire me and I was in severe mental shutdown. Luckily a friend helped me realise I had a problem, I got help and after a further 3 years I am much better. However it was a close run thing and I think if it had carried on I would have ended up dead. You have managed to realise you have a problem early enough that you can fix it.