[cannam]

I think you're right to distinguish between kinds of tiredness, rather than levels.

The article, good and thoughtful as it is, suggests that a dead-tired state is somehow just more tired than normally tired. But there is also a tiredness in which you are keen and ready and would be happy to get moving with something, but your mind and body are unable to do the real work competently - the analysis or the lifting. This is like your exhaustion, without your languor.

I had this feeling a lot during 2020 and put it down to a justifiable mental response to the times (I hadn't had Covid, as far as I knew) until, slightly to my surprise, I was diagnosed with a vitamin B12 deficiency which turned out to explain pretty much the whole thing.