Record your energy levels every hour on the hour. Make some kind of chart (using Excel, a Google doc, or a scratch pad) and set an alarm on your phone or calendar program to ding you every hour. You can come up with your own system. Maybe a 1-10 scale in which 1 is nearly dead (“dragging your sorry body out of bed” kind of dead) and 10 is Superman energy (ready to leap tall buildings in a single bound).