fine whine

Lately at work I've found myself closing my eyes to do a mental calculation*.

I don't recall doing this as a child, and even doing this months ago.

It's likely I've been a little more sleep-deprived lately than usual (though somewhat of my own doing) and work has been tenser and more stressful than usual (somewhat less of my own doing), but are those factors enough to degrade my mental abilities this much?

Also, am I sticking my tongue out as I do it?

* Well, actually I'm just doubling a measurement: seeing, for example, 11 7/8" and needing to write down 23 3/4". Why I now need darkness to concentrate on this simple task, I do not know.