It is nt to low a pulse! The average health pulse is between 50 and 70. When you are sleeping it gets lower still. Some spots people have pulse rates at 30bpm. If you are really concerned get a holter monitor put on for 24 hours and this will record your reading while sleeping.
I had one and my heart rate was 43bpm at one stage not all the time but at my deepest sleep point for around 2 minutes.
A low heart rate is good - if you don't get effected by its lowness, dizzy, passing out etc. It means that your heart only works half as hard as everyone elses and should last twice as long I say!!