I struggle with this.
I figured out that sometimes I can’t activate for ANYTHING because I’m not letting myself activate for the thing I want to do and am “not supposed to be doing.” Sometimes it works to just let myself zero in on the thing I WANT to zero in on, because doing what I want is better than torturing myself by doing nothing.
I also support what @MachUPB said about listing to music while working. Personally, I have ONE playlist that’s my “working” playlist. Actually, it’s not so much a playlist. It’s the mash up All Day by Girl Talk (EXPLICIT). If All Day is playing, I’m focused, and I don’t let myself listen to it when I’m not being productive.
Finally, I’d suggest exercise/going for a walk. Even if I’m not getting my heart rate up or trying to burn calories, going for a 20-30 minute walk in the sunshine can really help me ‘reset’ and get on track with something.
For me, the symptom of brain fog/paralysis/concentration problems is typically a “depressive” symptom, and I need to switch gears or get stimulated.