Thanks everyone.

Sally, what you describe seems very similar; as these episodes come on while I'm trying to do something or otherwise would be awake and fairly alert.
It isn't the cog-fog from fatigue, which unfortunately, has become familiar enough over the years to recognize.
Don't think it's from boredom either; as even when cog-fog is present, I have a rather 'busy' mind...and no shortage of things on the go.

Feels like everything just got unplugged again, like an engine running out of gas; and I am unable to push through it.
Something's definitely going on but right now, this chick's going to have to go lay down for a bit.

With love, Erika