I was with my parent at the end of life and that moment was a precious gift to me. In fact, I recall being asleep on a chair with my head on the bed when a change came over the quiet room. Strangely, I am no longer afraid of dying. I do miss, miss, miss her like crazy.
Take care of yourself. Talk to your mom. She knows you are there. The hospice staff is wonderful and very understanding. Lean on them if you need to do so.