It turns out that I'd been skipping out on slow-wave (aka deep) sleep, pretty often. A night without deep sleep just can't be restful. It's physically impossible. So that explains a LOT about my non-existent energy levels. As I've said before, I'm expecting not just more energy but a better metabolism and maybe even an actual decent immune system.
I'm looking forward to the point where I'm used to the device. I am looking forward to waking up refreshed—even more refreshed than I felt this morning, which I'm sure is just the tip of the iceberg.