There was a day, on a crossing to Hawaii, when we were windless, and bored. We knotted up an old sheet, probably a 3'4" braided line, and tossed it overboard with a fender on the end.
The sails were down and the boat was rolling gently in the low swells. I jumped in (sans lifejacket of any kind) and frolicked around a bit, only to find the boat was still moving, faster than I had expected. Thankfully, the line was within reach, and I began hauling myself back up to the boat, but it was a beast of a pull, and I was young and fit.
By the time I got to the boat I was so exhausted that I couldn't climb the ladder. Fortunately, I had crew aboard and they helped me up.
If you go over the side from a moving boat, unless you have superhuman strength, I doubt you'd be able to get back aboard unless she rounded up right away and you could easily get to the ladder. That leaves you a good flotation system and a radio to call for help.
I never wore a PFD, even in heavy weather, and didn't like harnesses, so I kept to the rule I was taught by some real, commercial Cape Horners, "One hand for the boat, and one hand for me." That never failed to keep me aboard, even in the worst weather. To me, a PFD offshore is only a certainty of a long and tortuous death, so I won't wear one.