Writer vs. Editor Mental Gap.
Dunno about anybody else, but if I spend the day writing, I'm usually refreshed for the rest of the day. Although if I push it too far, I'm wiped out. Go figure.
On the other hand, if I spend a good, solid chunk of time editing, I feel disoriented afterwards. I'm more likely to lose track of time while editing.
It's like the writer part of my head uses the dominant (creative, babbling) side of my personality, and the editor part of my head uses the next strongest (computerish, analytical) side of my personality--which means I have to shut off the dominant part in order to use it.
I think my creative brain is taking one of those naps that is both too long and not long enough while I'm editing, and wakes up groggy. I tried to talk to somebody outside of the technical writer group after spending four hours editing (tables, no less), and while the people in my group understood my perfectly, the other guy looked at me like I was talking baby-talk.
"Hm..." I could see flashing across his face, "She seemed at least reasonably intelligent earlier."