Zule...also keep in mind that completing your degree is sort of an initiation rite...a trial by fire. Other times and cultures used different rites of passage to mark various life stages...in a way, those were more straight forward and there was no mistaking why you would have felt exhausted...you were literally fighting for your life! Our rites of passage are much more ambiguous and, unfortunately, lack the sacred element of earlier transformational periods....but the archetypal remnants remain all the same. I don't know if you find this at all helpful...but when I made some changes in the way that I was thinking about what I was going through when I was in grad school....it made it a bit more bareable and put it in a better perspective for me.
You will come through this!!! And you are correct...your doctorate is killing you in a way...you will be a different person when you have completed it, just as if you had gone through a tribal initiation! Make sure to celebrate it, too!