For me it’s driving while under the influence. If you couldn’t tell, I like me some ganja. However I have long since held the belief that it is utterly insane to drive while under the influence of most substances, with maybe nicotine and caffeine being the exception. All too often I see other stoners smoking and driving, which I simply can’t fathom. I’ve only operated a vehicle once under the influence and it was just to move a U-Haul around the block to a different parking spot, which was such a scary experience while high that I refuse to even consider getting behind the wheel again while high.
There’s a lot of biology involved that I don’t understand the intricacies of, but basically the more time and at more depth you are underwater the more your body is dealing with changes in the density and makeup of your blood. You need time on the surface to normalize. For a similar reason you need to do safety stops to allow your body to adjust to the changes.
For normal recreation dives, it’s pretty simple that people are limited to (IIRC) two dives/two hours per day as a general guideline. Once you get into deeper dives, using different breathing mixes, and other stuff people have to start doing a little bit of double checking to make sure they don’t overdo it.