wow i feel a lot like you describe. I've been thinking about taking a few months off just to reset and somehow figure out what I want to really be doing but... it's scary. I have the money saved up for it to not be a problem. But after the 6 months... then what?
If you aren't interested in freelance work, try to look for companies with a dedicated research team. You usually won't find that in smaller companies, as they cannot afford a few people trying to solve a problem for 2 years with only a 60% chance of success.
PS: if you are really unhappy with your job (to the point where it affects you physically), don't think it will magically get better if you stay. It won't. This hope wasted 1 year of my life.
What did you end up doing? Any advice?