MtheGM says "...gone upstairs to fetch something, thought of something else that needed doing while up there,..."

That's called the "butfirst" syndrome, and is quite common. Everything you start to do requires that "butfirst" you have to do something else in order to get to the original plan, but first there's another butfirst to do before you can get to the first butfirst. This cycle sometimes seems endless.

The related syndrome seen frequently, but not exclusively, in the elderly is the "hereafter" effect, where one walks into a room and has to stop to ponder the hereafter ("What the $@%%#! did I come in here after?)

The combination of the two, as you've described it, is actually quite efficient, since there are nearly always enough "butfirsts" that eventually the "hereafter" doesn't really matter since one nearly always discovers sufficient "butfirsts" that are more important.

John