[zapperdapper]

> I've decided I need to quit.

OK fair enough. But ... have you tried various options first within your current job? Have you asked for an extended holiday? Could you change your commute so you cycle in at least part way? A four day week? Have you looked at your schedule and tried to add more exercise? Are you sleeping 8 hours? Have you asked for a sabbatical? (ARM for example will give you a paid three month sabbatical every four years.) I say this because you said at one point you loved the work. You might just need to shake things up a bit.

If you really decided to move on then lots of good advice here already...

[techexecadvice]

I haven't asked for an extended holiday. I'm worried about making such a big ask of my boss (our culture is not very progressive) and then coming back only to quit. What do you think?

[zapperdapper]

Why is an extended holiday such a big ask? - would they rather give you that or lose you to ill health? What you could do is just quit, take a few months off then start applying for a new job. I would have thought someone with your level of experience could easily find a new gig. Only you know your exact situation.