Heart Rate upon waking can have some significant variability. If you have a full bladder, or were awakened suddenly by an alarm clock, you may have an elevated heart rate. Your heart rate also varies considerably while you are alseep corresponding to the various sleep levels. If you have a access to a high end Polar heart rate monitor that records heart rate data for download to a computer (S710, S720, S725), wear it overnight. You'll be amazed at how active you are while asleep.
BTW, a 42 bpm resting heart rate is very good and something to be quite proud of.