When I was an FO on a 767 the captain climbed to FL430 for a smoother ride. Soon after level off we were advised one of the passengers had passed out and was put on oxygen. Ten minutes later the captain went back to see how the passenger was doing. I checked a few airports ahead of us and found one that would work for a possible divert. When the captain came back a few minutes later the passenger passed out again with oxygen on so we diverted and once on the ground the passenger wanted to continue with us but we left him there.
I have had similar situations many times and always get a lower altitude as soon as possible to get the cabin altitude down and have always continued to destination. That one divert cost the company more fuel and inconvenience than the fuel I burned the next 15 years using a lower altitude to help the situation.