I don't have a meter (that I know of) in the actual sense, but I call these days "low battery mode" and yes they do happen mostly if the couple days prior have been eventful in one way or another - whether stressful or blissful, that doesn't even matter. On paticularily bad "low battery" days, I don't even feel hunger/thirst and have to force myself to eat and drink the bare minimum. Literally everyhing is a slog for a while then, even things that I normally enjoy. It usually takes a day or two to get better on its own.
....and yes, trying to explain these things to someone who has never experienced the issue firsthand is very difficult. People usually assume I'm just feeling a bit down and need cheering up, not understanding that the things that normally would cheer me up do not have ANY effect at the moment, and that I'm not "feeling down" but don't feel anything at all.
Sadly I haven't found a good way to cope with the issue except for waiting it out until it goes away.