I recommend at least 3 days off if not 4 or 5. When I get to this point, I veg a little, and try to do some active mental rest like a quality, make you think podcast or chess.
Feel you on the low points, thanks for sharing, it's heartening and motivating to see people who are struggling show that kind of positive mental attitude!
I think Sudoku type puzzles are great and exercise a lot of the same mental muscles as LGs. You have to treat them like outside reading though. They're great extras, just don't treat it as study time.