I am considering quitting my job when I don't have another job lined up?

I am currently employed full time but hate it and am considering quitting but I dont have another job lined up. I recently lost out on a job offer purely because I couldnt start straight away and the other candidate could as she didn't have a job at the time. I am also wanting to get a mortgage early next year so dont want to risk losing that aswell. I am really unhappy in my current job and it is also starting to affect my health and I dont know how much more I can take. Please can someone help?

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