I think this was all because of not getting enough sleep the night before.
Tonight, at least, I've slept enough - in bed at 10:30 (after nearly falling asleep on my feet at 10), awake at 6:50, in bed hoping to fall back asleep until 7:30 but feeling good for a change. Whew. I even brewed a cup of tea this morning, and the very sweet
Tonight: All About My Mother at the Old Vic with