I get these fluctuations too. Some days I'm so lethargic I can't even lift my head from the pillow. I sleep for days, only getting up to eat and use the bathroom if I have the energy.

Other days I'm wide awake, I can't sleep for being so wired.

Sometimes I'll start the day feeling energetic only to crash out of nowhere.

I don't think I've ever felt mentally focused since though. It takes me several efforts to write things and almost always I follow effort with a nap.

I don't think much is normal or consistent with TBIs unfortunately.