Your effort will be uneven. Make your standards a lot less uneven than your effort.

Energy varies for reasons you do not control, and no amount of planning makes every day equal. Standards are different: they are a decision rather than a supply, so they can stay roughly constant even when what you produce is thin. Holding the standard on a low day may mean doing less, done properly, rather than more done badly.

On your next tired day, cut the amount rather than the care. Do one page or one drill to your usual standard and stop there. Decide in advance what the small version of each commitment looks like, so you are not inventing it while exhausted.