I can strongly relate @LetterBetter - I had a TAH and BSO at 42, like you, I was childfree by choice, in indescribably bad pain from endo with multiple adhesions, adeno and fibroids. I had known for a long time that I didn't want children, and even if I'd had a change of heart, I was at the tail end of my fertile years.
But there was a finality and irrevocability about the decision that gave me pause - I suppose it could be described as going from 'childfree by choice' to 'sterile' - the 'choice' element was being removed from me. I also had concerns, especially as my ovaries were going too, that I would lose any capacity for sexual pleasure (I'm 10 years down the line now and can assure you that did not happen.)
The feeling of being 'struck' by coming sterility was just a temporary feeling, wrapped up with general apprehension about the surgery. The pain I'd been in before the surgery was so bad that, within about 4 days of the operation, I was in less pain than I'd been in before it, even with a healing wound.
The freedom once I had fully healed was marvellous, a life no longer governed by pain, no longer having to plan everything round my menstrual cycle. It was the best decision I've ever made.
If you're at all like me, the feeling will pass, and - it's hard to explain - I think I had to mentally acknowledge the finality of that decision to rule out any future regrets that I had gone into it without considering the implications. When I went under the knife I knew I had fully considered that it was irrevocably committing myself to a life without children, I had processed it and I accepted it.
That's rather confused-sounding, sorry, but I hope it's helpful, and I wish you the very best for a smooth procedure and good recovery.