Orange juice has potassium. Other potassium sources include tomatoes, bananas and the lowly potato. One of the things I like about Hydralite (formerly Gookinaid) is that it has plenty of potassium and not as much sugar as many electrolyte drinks, plus a mild tart citrus flavor. Things that are too sweet tend to turn my stomach. Of course you can make your own electrolyte mix using, among other things, "lite" salt (potassium chloride) (recipes on the internet), or use medical hydration salts, but it really helps to have some flavoring! To me, the flavoring is more important than the "spoonful of sugar [that] makes the medicine go down."
I've seen people bonk using sugar for energy. Climbing up 3,000 feet to a pass on a west-facing open slope on a hot afternoon, the 6-foot long-legged guy who was using candy for energy kept having to stop for more. I'm usually the slowest (by far) in a group. In fact, the only "hiker" slower than me is one of our Oregon slugs! On this stretch though, I passed him every time he bonked; about 20 minutes later he'd pass me; in another 20 minutes I'd pass him again. The mechanism, of course, is that the excess blood sugar from the candy kicked off the insulin glands in his pancreas, and the resulting rush of insulin lowered his blood sugar. I've been told this is a really good way to bring on Type 2 diabetes. I mention this phenomenon, Newton, because you said you'd been eating mints during your workout. Consider more complex carbohydrates, which release sugar more slowly and generally more evenly.
In your case, Newton, like the others here, I also suspect not enough calories plus electrolyte (other than salt) deficiency. You mentioned that your dinner the night before was mostly fruit--just remember that what you eat for dinner the night before is what is most available to your body during morning exercise!