Stress
Nope. No stress to be found here. Not in the extreme isolation, not in the possibility of malfunctioning equipment, not in constant fear of a shark attack (those things are stealthy). Oh, wait—yes. Yes, there are a ton of potential stressors in this field.
Commercial diving is dangerous, and your paycheck is generally a reflection of just how dangerous you're willing to let it get. Imagine if McDonald's worked that way: "We'll pay you eight dollars an hour to flip burgers, or we'll pay you twelve dollars an hour to flip burgers with boiling hot fry grease balanced precariously above your head." Are you the kind of person who likes to up the ante on such things?
Knowing that mistakes can cost you your health (or your life) is never a recipe for a casual, low-stress work environment. Messing up can endanger you and your workmates, which means it's crucial to pay attention, even when you're doing what's otherwise mundane work. Multiply that by about ten when you're diving HazMat-style into toxic sewage, or into the irradiated water of nuclear power plant.
Even if you forget that stuff (although how you're forgetting an afternoon swim through sewage is beyond us), being a commercial diver can be taxing on your life outside of work. Often, jobs require you to stay on a boat or in a cheap hotel for weeks on end while a job gets done. That places massive pressure on your social life, romantic life, and parenting life—and that's a lot of lives to be stressing about.
All that said, much of this stress is going to grow or shrink depending on the type of person you are. If you're a fearless loner who lives to dive, you can pretty much forget most of what you've just read. Except for maybe the sewage bit. Yuck.