I used to just walk away from it...just like when cramming for a test, you can take in too much info, or just get stuck.
I've walked away for a few days or longer...take the time off though to do some paperwork...a.k.a sheet music. OR get online and read up on your theory.
2nd option is like you stated, try learning a new style...if your into metal...learn some old mo'town 70's funk. Start youtubing some bass solos and watch guys that are out of your norm.
It happens to us all..hell I'm 40 and still get in them. I just broke out all my theory books after putting them down 10 yrs ago
