This was a few years ago on a night scuba dive. There were 8 of us in the group including our dive master and his assistant. We had just finished our dive and were gathered up in a circle ready to ascend and get out of the water when my dive master freezes. He takes his flashlight and pointing it outside our circle of divers he catches something circling us with the beam. Turns out it was a 12 foot long great white shark. At this point half of the group are trying to keep the shark illuminated as it circles us and remarkably everyone stayed calm. The only things going through my mind were iterations of these two thoughts, "don't look like a yummy delicious fatty seal, and that I hope I taste terrible." My dive master gets our attention and slowly puts his thumb up and then makes an upward motion. We all begin to ascend and the shark kept with us until we were maybe 10 feet from the surface. Then it turned off into the darkness and was gone. I did not go back into the ocean for about a week after that.