What really helped me "recharge" the CNS was Medicine Ball Training on your recovery days at least 1 time a week. I would do a plethora of exercises with a light MB as well as multiple core rotations within a 30minute time frame and the results the following days was amazing.
I hate frying the nervous system. Obvious sign of over-training and it sometimes takes a while to bounce back to that 'normal' level again where you can push yourself again. Cycling workouts with new exercises allows the CNS for specific movements to recharge as well...there are many factors but everyone's body is different, the trick is to find the exercises/rest/diet/recovery work that recharges the CNS.