When I was healthy, slim and fit, I got my RHR down to 34-35 bpm. As I got fatter and slower, it gradually went up to 55-60 bpm, so for me it was a good indicator of how fit I was, or wasn't! You can only compare yourself to yourself though - 50+ bpm is high for me, but it is probably low for a lot of people.
I haven't measured my resting heart rate for a long time, but I did notice that I was at about 60 bpm in hospital recently when I wasn't feeling stressed. Any hint of stress and it shot up into the low 100s. (They did regular blood pressure tests and the device had a heart rate readout. If a consultant was telling me scary stuff, my blood pressure and HR reacted almost instantly.)
Just before I went into hospital last year, my RHR was about 150 bpm and it stayed like that for hours at a time. (I wasn't physically capable of doing anything, not even watching TV or reading.)
Short-term increases in RHR can be a good indicator of impending illness or overtraining, so if your RHR is elevated, take a rest for a day or two and see if it comes back down.