Switch or Fan going bad?
Without a photo I am guessing that the switches are stacked in a single gang box in this case there are 2 witches on 1 yoke, of side by side they would be in a double gang box and be 2 separate switches. It is possible the switch or the wire connection failed, I usually check by spinning the fan and turning the switch on if it keeps going it is usually the fan start capacitor that has failed.