Having a long-term record of your resting heart rate (with or without HRV) might be useful. If you exercise regularly, heart rate recovery time could be another useful measure to collect.
If your heart rate doesn't adjust properly when standing up (a fairly common problem), that's something a doctor can test easily during a visit.
When you see the specialist, ask what kind of measurements would have been useful, and report back!
Regarding RMSSD, all I know is that if the value drops below zero, you have faulty software