Another data point:

Yesterday I went on the 60 mile ride again. I felt tired before the start, and didn't really want to ride, but in the interest of science, I went.

I was more tired at the end than I was last week, but not that crazy tired feeling.

Of course it could be a placebo effect. Fifteen minutes into the ride I felt good and thought, "Well, this electrolyte stuff really works." Then I remembered that I hadn't had any nuts yet. It would be good to do some real double-blind testing, but that's too much work.

But this second ride supports the idea that my electrolytes have been too low in the past, and that I can look forward to stronger rides in the future.