What's that saying, "wherever you go, there you are"?
How much of your misery is recent? Have you enjoyed other jobs in the past? Are you happy away from work? When have you last had a holiday and was it a proper break?
There is a stage of MMM that a number of posters seem to go through when the prospect of work being over in eight years time makes it more miserable today. This phase passed for me, YMMV. (If you feel genuinely depressed, see a doctor sooner rather than later.)
If you have considered all of the above, and you think that a sabbatical is the answer, go!
Have you considered going further? Check out WWOOFing, cheap COL countries, go see Europe before Brexit!
There is nothing wrong with you for being upset and miserable at work. There is something wrong with your life if you are upset and miserable.