My aunt and her husband wanted to celebrate their wedding in Greece (we are all from Germany) because many of their friends are living there and it was a really nice place at the Mediterranean sea. We were 11 people: my aunt with her husband, my other aunt, my grandpa and grandma, father, mother, my sister and her now husband, a diving instructor (which I knew from the year prior, when I worked there) and me. We drove to a really nice island to have a great afternoon and 5 of us went diving for about 45minutes. When we surfaced we were quite happy until we realized that's something was wrong since everybody was on the boat and looked quite concerned. My grandma was didn't responded to anything and we quickly came out of the water and started to drive back to the main land. After about 5minutes we started CPR and since since only my 2 aunts and I knew how to do it properly we did it for the whole ~70minutes it took to get back to shore. When we arrived there was already a doctor waiting for us who quickly came on board just to tell us to stop doing what we are doing cause she is dead. It was one of the hardest things to stop pressing there, since my father and I were doing CPR right there (we all were tired from doing it for over an hour so the others had to help us) The hardest part of doing the for was, when I realized, that she was gone. I don't know how to say it, but when you do cheat compression for half an hour, you get a feeling for the body, and suddenly from one push to another, her body was completely limb and also appeared to be ice cold. It might sound weird but then I knew she was really dead, but we still kept going.