Your story reminds me of one incident some long time agos.
I was a DM Trainee back then, joined on a Liveaboard trip that my Dive shop organised in West Coast Thailand.
On that trip, there was one customer who'd joined the trip solo. He was quiet and pretty much enjoy his owned company. One thing that make everyone on board noticed him was his wetsuit. Full long sleeve in Bright Orange color. He was not in the group that I'd assigned to, though. His dive skill was ok to good.
Last morning on that trip, I woke up to find this person enjoying his coffee on open deck before everyone else, with a crew/deckhand watching him with strange look. So I approach the deckhand and asked what's going on.
The deckhand told me that he was on late-night watch duty. The boat was tied to a mooring point in a calm bay. The customer in question get up at around 04:30hr, put on his dive gear, and went diving alone for about 10-15 minutes. The deckhand was not at the dive deck when he went down, but came to see him enter the water and watch until he come back up.
The deckhand also end the story that, when the customer come up, he wetsuit was totally filled with SXXT...
I'd never saw that customer since the end of that trip.