I measured my RHR this morning after drinking a glass of water and having a BM but before my morning gut buster (workout). I laid down on the floor and took a few measurements for a full minute each time. 39 was the lowest count and 40 was the highest. Deep, steady breathing helps to bring it down.
Overtraining can raise your RHR so if you are doing heavy/frequent/voluminous training it would be a good idea to monitor RHR over time every morning. If it is decreasing or staying the same then you are not over training but if it begins to creep up then that is a sign to back off on the training (IMHO).
Something I picked up from Gordon Pirie's online book "Running Fast and Injury Free". He was the Brit who won the 5k in the 56 Olympics and had the 5k world record for a while.