Getting back into the swing of life after a breakup

I thought I'd ask the question in here.

Few weeks ago me and my girlfriend broke up, was a largely mutual decision with no blame attached to either side, it just wasn't working and we were unhappy.

Since then I've regressed from being a 38 year old man, to basically being in my early 20s.

I've been seeing friends for pints, going on nights out and just not taking care of myself at all. McDonalds for lunch, not bothering to go to the gym/exercise in general.

I'm aware this has a finite shelf life because otherwise I'll like have a heart attack but I'm just not totally sure how to get myself going again and getting back to living relatively healthily, exercising and actually working during the day instead of going on reddit.

Does anyone have any tips for mindset shifts or things they've done to just get their shit together again?