Thanks for asking, u/dogsetcetera!

I switched to what seemed to be a much better re-hydrator/electrolyte tablet. It seemed to work almost instantly.

The 'odd' feeling did come on - about four hours after I had breakfast and drank 16 oz of the Nuun. So I had a couple of small snacks.

The 'relief' - again - was almost instantaneous!

I can't help feeling this is low blood sugar or some other kind of depletion.

I guess I need to be prepared to eat when the feeling starts - or even before, regular meals - because that's what my body is telling me.

Presumably it's why runners carbo-load?