Our guys get rambunctious and grumpy during upgrades. Their sleep stays the same, but they cooperate less.
It was most noticeable when our older guy got reading. In the space of a few weeks he went from haltingly sounding out words, to (hesitantly) reading strings of words. Maybe it wasn't that dramatic, but I remember it that way. It was late winter and around the same time he decided he didn't want to wear winter jackets/mitts and he didn't like food we prepared for him.
I didn't really correlate the two until after.