You lost one side of the RV. Is your rig a 50 amp? is it plugged into 50 amp or 30 via an adapter.
First part of this applies only to 50 amp RVs
Check park outlet and breaker.. Most people think that those dual ganged breakers both trip at the same time. NOT TRUE. it is possible to trip one without tripping the other.
Outlet may have "lost" one connection as well
50-30 amp adapters often drop one of the 50 amp legs as well. Try a different adapter.
You can also have a screw loose.. Mine was on the power INLET for my 50 amp RV, along with several in the circuit breaker box.
Auto Transfer Switches can do it as well.
Next This applies to ALL Rv's
If you have an inverter there will often be either A: A curcuit breaker or two on the inverter that may have tripped (There was a woman here once who had the same problem you have. She thinks I'm some kind of wizard.. I reset the tripped breaker, that's all, anyone could have done it). Sometimes the inverter feeds a SUB panel, (mine does) I do not, however, suspect an inverter in your case.
Screws loose in the breaker box can drop one side, the other side, or specific items (A/C's in my case)