If you monitor your resting HR as well as your HR and perceived effort on rides you can get a good idea how your body is doing at any given time. If you are unable to raise your HR on a ride and your RHR is higher than usual or trending higher you need to rest. If your RHR is low or dropping and your HR on rides is not reaching the higher ranges, you might just need to switch up you riding efforts. A body doing the same type of exercise daily gets stuck in a rut. Maybe it's time to hit some intervals, shorter duration but higher intensity.

As Hermes said, be sure to schedule periodic rest weeks to allow recovery and adaptation.