my new low resting heart rate!

I did a heart rate test on myself last night using the hr monitor all night and it came out with an average hr of 47!! Is it normal for your resting hr to drop that much after 6 months of tri training? I am definitely NOT complaining, just wondering how accurate these results are. When I started training last march it was around 61 so it is great to see that my cardio fitness is really coming along!