I have to agree with IAG about being there at the time of passing. I was there with my dad. When he entered the hospital that last time, none of us considered the fact that it was the last time. He had been diagnosed with cancer less than a month previously and his biopsy was scheduled for a week from the night he entered. He fell at the house and mom had to call 911 because she was unable to lift him. Since he was in pain, they took him in to check for any possible broken bones. He was dehydrated as they discovered. My sister and I were in Florida at the beach, on the family vacation my dad had planned. At the last minute on the day we were to leave, he announced he just couldn't go and we should go on. It took an hour of arguing and tears before we agreed. We left on Saturday. On Monday morning, Mom called to tell us that Dad was in the hospital but for us to stay and she would keep us informed. She called us on Thursday morning to tell us we needed to come home. I knew when she called that this was that moment.
Everything that the doctor had done since Dad entered the hospital to help him had not worked. The doctor told us he was a little flummoxed with the situation and did not know of anything else to do except help make sure he was in no pain. Except for a trip home to get Mom more clothes, I was at the hospital from Thursday night until we all left late on Sunday night. On Saturday, we each took time with Dad, holding his hand and talking to him. Basically giving him our permission to let go, assuring him we would be ok and we would take care of Mom.
We (my mom and sister included) had been told it could be anytime, which could mean 10 minutes to 2 weeks or more. But on Sunday night, we all noticed a calmness. I called him remaining sister and told her that we felt the end was coming. Her son drove her up there. Dad grasped Mom's hand. His sister arrived and sat beside him on the other side, telling him she was there. In 15 minutes, his breathing just stopped. We were grateful he didn't suffer.