Sometimes taking a little time off helps to motivate me. If I push too hard, I can get burned out fast and then it's not fun--it's something I "have" to do. Taking a break seems to do the trick. Sounds like you might need a few days' rest to get healthy too. If you keep pushing yourself, you may never get over your illness or, worse yet, get worse and miss more cycling days than necessary. Being sick always gets me bummed out too.

Hang in there. You will do fine on your 50-miler.