It seems that, with great effort, I can manage one modification to my schedule at a time. For a while there I was doing pretty good about getting eight hours of sleep most nights, which was a nice change, making me feel a bit better throughout the day. So, I decided to ruin it and try to also get back into a more regular exercise schedule, so I could feel awful during the day again.
Two schedule modifications are apparently too much for me to handle; I'm now doing poorly at both. (As you might guess, I plan on getting up less than eight hours from now.)