Hello Dear and thanks for writing in
In my opinion you are suffering from Chronotropic Inefficiency. Heart rate
below 50 in day time and below 40 in night during sleep is a matter of concern and may require immediate Pacemaker Implantation(PPI). This device paces the heart when needed and do not allow the heart rate to do down below the setting usually 60 bpm.
Get hospitalized and go for Temporary Pacemaker Implantation and Holter examination together. After the holter report if any sinus
more than 3 second is noted than you may need PPI.
Other causes are Medications like beta-blockers and Coronary Artery
Disease. Consult your Cardiologist as soon as possible.