I can relate somewhat although as you can see we all come to this issue from a different view point.

I too have been in a place that most people label depression. I could no longer grab onto something with meaning. An antidepressant can lift the heavy feeling, but doesn’t lift the soul. I never stopped smelling the roses - that wasn’t the issue. I also functioned at work and doing things for and with the family. You mention lack of self discipline, but the fact that you’re functioning beneath the radar indicates you do have a fair amount of self control - there are lots of people that can’t even accomplish that!

I can’t tell you what exactly has finally changed my outlook. I think it was a series of events causing me to re-adjust my life, and therefore re-think my view. From stepping away from a very destructive work environment, to my mother’s death, to dealing with mental health issue in a family member.

But I do know a major impact was a book that I’ve mulled over for a while. Written by Dr Gail Brenner, it discusses how to move past regret, how to deal with emotions perhaps triggered in daily life. I couldn’t absorb her whole message, but I’ve read/listened (audiobook) to it enough that small steps are helpful.
This is not a new book, and her message is not trendy. It’s not zen or religious based. It’s how to deal with the now (and stop trying to fix it over and over).
“The End of Self Help, Discovering Peace and Happiness”, by Dr. Gail Brenner.

I wish you peace, you’re not alone!