I can relate to this a lot. I switched groups in the fall, also in my fourth year. It was terrifying and I took many long walks just evaluating everything in my career plan to see if it was worth it or if I should drop out or what. I wanted to switch mostly due to conflicts with my advisor and not making much progress on my projects due to experimental difficulties.

I ended up getting a master's with the work I had done on the project so far, and switching to a new advisor and research project, and I'm planning on doing my prelim exam next month. Let me tell you, I feel SO much better now - my new advisor is so supportive, my experiments are going well, and best of all I have a plan to graduate with this new project next year, so no delay from my original degree plan. Also, this was my second time switching advisors as the professor I originally started with left the university.

It sounds like you already know what you need to do, so I encourage you to do it and know that it will get easier when you're settled into a new group. Definitely take some time to destress now and figure out all your options before you go for it, but don't stay with a project that makes you miserable.