Aside from a physical problem /heart attack/passing out/any health issues that render you helpless,, there are a couple of things I try to keep in mind....barred of being knocked unconscious during the fall.
I always ask myself how would I try to exit if I fell.
I fish some cliff like structures and those, to me...are the most dangerous. Getting washed off by a mini-rogue wave while landing a fish etc. In those areas, there's always the chance of hitting your head on a rock, whether it be while falling or the waves picking you up and dropping you on them.
One MUST feel safe and comfortable at their fishing location. If you don't feel safe, your probably not. MAKE yourself safe. Whether it be backing up a bit, getting on a different rock or simply going to another spot all together. I drive long distances some times just to find out that it's NOT fishable the way I'd like to fish it...sucks-but it happens.
I also feel you SHOULD feel completely comfortable in the water itself...meaning NO FEAR of swimming at any depth or condition. Obviously you don't want to be swimming out there in a Nor'Easter but you have to keep the realization that you may fall or trip, you must remain as calm as possible, TAKE YOUR DEEP BREATH....ACT FAST and get that breath again until you've figured your way out of your dangerous situation.
I've fallen in water over my head while wearing waders. I knew I was going under so I held my breath during the fall. I had enough air to act quickly while at the same time make timely efforts to get air until I was safe. You can't PANIC.
Chatham SandBars in the fog
...of course that can happen on any given beach but it was Chatham where I didn't know where the shore was. Every direction I tried, it got deeper. NO compass (who in their right mind is that prepared?? Not me. I came to the conclusion that if the water rose enough, it was time to shed the waders and figure it out in my skivvies. I LOVE the water, which I really think helps my comfort level...but probably makes me take more risk.
It's also easy while wading in the dark or light, to position your foot in a bad spot. Just before a rock OR just after. You can't see the rock but you'll feel it as soon as you try to move forward or backward...and if you trip, you have to realize that you're going to get wet. Don't panic, get wet...but get up. Don't worry about your gear until YOU are safe. Gear is replaceable....you are NOT.
headed off to work, I'll add more shtuff later if it's not already mentioned.