Loren,
Unless one or more jacks are down as Jerry states, you have an air leak. The leak can be at an air bag, an air line fitting, one of the valves, an air line (unlikely), or one of the solenoids. The leak will be in connection with the low side, but not necessary the lowest point. If the RF is your lowest point, the air leak may be in the RR.
Normally, a suspension air leak that takes 3 or 4 days to be noticeable is not worth the time and effort that is involved in locating and repairing, and most of the time is normally spent in locating it. However, if the suspension leaks down badly overnight, it should be repaired if possible.
Gerald