I'll relate a couple ...
The first was in Bali ... when I was a reasonably new diver (about 80 dives or so). There were four of us on a charter boat out of Nusa Penida, going out to some little group of rocks a ways offshore. Short version of the story is that we encountered a strong current and got blown between two of these little "islets" and surfaced on the opposite side ... where we and the boat could not see each other. The current continued to carry us further away from these rocks ... and after about 20 minutes or so we were quite a long distance away. The boat was still on station on the other side, waiting for us to surface. After another few minutes we spotted a fishing boat and waved our arms ... hoping to flag him down. He waved back and kept going ... disappearing behind the rocks that were now barely visible in the distance. A few minutes later our boat came out from behind the rocks, heading toward us ... the fishing vessel had informed them that their divers were getting away. Overall we were on the surface for about a half-hour or so ... and the most worrisome part was that our dive guide was shivering so badly we had to help him up the ladder.
The second was a local charter ... in the San Juan Islands. We were diving a double-island with a small channel in between. The charter captain had briefed us that we would be able to see the channel, and were to avoid going between the islands, as the currents would put us on the opposite side of the island ... and it was rather rough conditions out there. We did our dive and boarded the boat ... all but two of us, that is. The plan had been for a 60-minute dive ... and after 70 minutes had passed I mentioned to the captain that he should check the weather side of the island, because the two missing divers were unlikely to blow their dive plan. He insisted on remaining on station, pointing out that they had plenty of gas for a much longer dive. Another 20 minutes went by ... at this point, I'm practically arguing with the captain to go check the other side of the island. I'm worried, because the weather was getting bad and the waves were crashing onto the rocks pretty dramatically. About that time, one of the missing divers appeared on the island ... walking across the top from the opposite side. He and his buddy had been on the surface getting pounded by waves for over a half-hour, and he finally decided to ditch his rig and swim to shore, walk across the island and hail the boat. Now came the tricky part ... getting back in the water and swimming out to where he'd left his rig and buddy, so the boat could pick him up. He ended up getting bashed around pretty good, put some holes in his drysuit, and generally wasn't a very happy diver. According to him, you could not see the other island as you shot through the channel ... and they had no idea they were on the other side of the island until they surfaced and didn't see the boat ...
... Bob (Grateful Diver)