My husband is 42 years old , 5.10 and weights 75kgs. He is healthy with no medical issues like bp or diabetes etc. His pulse rate during the day while doing normal activities is around 75-78, while sitting n watching tv or reading it's around 68, however when he is fast asleep in the night it goes down to 57-58. Have read normal heart Rate should be 60-100..since this is below 60 Is this a cause for concern?