I guess if I am honest I would have to say pain.
I had an industrial accident when I was 19 and my hand was cut more or less in half.
There were some mistakes made in the emergency surgery that ended up amplifying the pain level by about 15x. When you are talking amputation that is a lot of pain. They also got me addicted to pain meds and tranquilizers.
At one point I even played Russian Roulette fortunately I stopped after the second click (.357 mag).
It was a very long time ago and I have had great joys and sorrows in my life but I will never forget that all consuming pain.
After 21/2 years I got lucky and got a great Dr. He did a major reconstructive procedure that was supposed to be rather painful. But he took all the wire out of my hand and after the surgery all I wanted was an aspirin.
Even now, almost 40 years later, it hurts constantly but one learns to ignore it.