Should I stick with a job I hate?

I've been working at my company for 4 yrs. I absolutely hate it, I hate no interest in my job and don't see a future. My bosses are total tools and intentionally give everyone low reviews so they don't have to pay them more and bully employees that speak up against some of the practices that gone on (i.e.: lack of cross-training). I know the economy is bad but I think I'm better off taking some time off. I feel I've reach my apex in my company and I need to go back to school for a MBA to actually do something with my life that I enjoy. I'm just tired of dreading having to go into work. I'm fortunate as I have a good amount of savings, no mortgage, and single. The job has caused me health problems too: depression, obesity (I've never been overweight before), and just high blood pressure. I just think it's better for me to leave now than have this job and company be the end of me. Thoughts?

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