A person can dive immediately after flying, with some advises such as drink lots of water. Usually we see the "rules" about not flying for 12 hours (some says 18 hours, some just say not the same day) after diving. Then there are stories of people "violating" these and fly soon after diving. What happens if someone flies too soon after diving? Is 12 hr a hard rule, or if someone dove using Nitrox could it be shortened to 9 hr? This is with "regular" recreational dives, going on guided tours with divemaster.