The problem is you shouldn't get very tired. Weakening the organism in general works in favor of infections/virues. On the other hand stef2011 said you need to do regular exercise but an easy one like a longer walk or something like that to help natural immune response.
I was riding until I crashed hard, kept falling and went into HE phase. Now I'm scared to ride, but I go to Y once/twice a week and ride stationary bike. Can't fall off that one. Do what you want until it becomes impossible is my advice.