Most people apparently have their lowest heart rate first thing in the morning, but a minority, including me have their lowest last thing at night. My rate is easily 15 bpm higher first thing in the morning. The lowest I ever recorded - several years ago now - was 34, though 36 was more usual. Take-home message from that: it is not your pulse rate that tells you how fit you are compared to other people, it just tells you how fit you are/were compared to yourself on another occasion.