I'm currently in what we call a longer-term up-swing. That means I have more than usuall "good" days -- a measure of my brain energy. The scale goes like this:
Good: able to hike/trail run, think and write more clearly, handle some minimal extra stimulation (like kids hollering). I fade as the day goes on.
Medium: I can make the half-mile round trim walk to the post office, if I do it by 10am.
Hard: (there are no "bad" days, just hard ones!). Like today. I can't do much. Can barely make it to the next room, or do much writing (as in complex plot, characters, etc).
Clearly my brain is recovering from something. Today is a day of rest -- part of the reality of going as fast as I can, as slow as I must.