I went from a typical 9-5 job to working part time, about 16 hours, to focus on my studies. Doing this increased my overall happiness by a massive factor. Being able to spend the majority of my day on something I was actually interested in and passionate about pulled me out of a "life is meaningless, why bother" mentality that my former job had buried me in.

The pay cut was drastic, but I was lucky (in a way) that I had come from having nothing the majority of my life so going back to almost nothing was an easy transition because it was essentially my 'default mode'. And even when I was making a considerable amount of money, lifestyle creep never became an issue. I lived well within my means. This is important because this combination allowed me to actually quit my job and live off of savings for years while I went back and completed my undergraduate. I've had friends in similar situations who have had to go back to a job they hated because they couldn't adjust. But for me, it was worth cutting every single cent and I will never work a 9-5 ever again.