Yesterday I wasn't really worth anything productivity-wise. I noticed myself just drifting through the day, falling in and out of sleep for parts of it. This morning I woke up around 9:15am. I'm usually up and around before this so I know I was pretty tired.
And that's OK. My body is busily being altered by my chemotherapy so of course it's going to be tired. I'm not mad, upset, or angry at my body. It's doing what it can do. All I can do is just let it do what it needs to do and not try to fight it. Whatever I wanted to do can wait; taking care of myself is first and foremost on my list. (I even added a task to my next actions list called "Rest" and gave it the highest priority).
Being OK with what your body is telling you is key to allowing yourself to heal and be ready for whatever might come your way. Sure, it can be inconvenient and a bit rude about when it wants to curl up and sleep, but that's your expectations running counter to what your body is currently capable of handling.
Give yourself the rest if you can. Sooner or later your body will collect it anyway.