One of the important reasons that on a windy day you never cleat your sheets. The jib maybe if you are solo, but never the main. Just saying. Not being critical, just safety aware.
As you say, sailing solo so the jib was cleated. Mainsail was not. I have a bit of weather helm on the boat, which is why she luffed. Even not cleated, there's enough friction on the main sheet to cause problems.
Biggest frustration I have is that I had the main sheet in my hand. I should have held onto it. Instead, I start falling, let go of the main sheet and try grabbing for something else. Anything. Yeah, like that's going to happen. If I'd held onto the main sheet, I probably could have created enough drag to slow or stop the boat.
Best of luck,