[kansando]

When I was in grad school, I went through exactly what you are experiencing. My advisor sat down with me and said:

"Take a month off. Go hang out with family and friends. Don't think about work. Eat well & exercise. Then we will talk."

It was the best advice I ever got. I realized while I was away that I was working on the wrong problem, and that with some reframing there was a way out. You can't get that perspective while you are in the middle of things.

[timr]

You had a good adviser. Mine would grudgingly look the other way if I took a couple weeks of vacation (at best), or become actively hostile (at worst).

In any case, it's excellent advice. The only reason I was able to finish grad school was because I took a couple well-timed vacations when I was in exactly the mental state that the OP describes.