Happened to me many years ago except I didn't fall off. I was a deliberate step around the stern of my dinghy. Didn't quite expect to be stepping off the dock.
At night, 'W' pier where you could tie up freely for it seemed as long as u wanted (that is another story entirely), winter, wet weather gear on cos it was blowing a hoolley and raining , on my jack jones, but the worst of it was - holding a 'new to me' 8 horse long shaft Merc outboard that I had bought from fast eddie the outboard guy in Ellerslie (used to be a Miller Moyes place there by the motorway and the guy worked there. TB