Low heart rate (Bradycardia) can be physiologically normal (i.e in Athletes), or it can also be due to various causes.. for eg. Hypothyroidism, certain heart diseases or even drug induced (beta blockers, etc..) Does the blood work includes thyroid level? Hypothyroid could cause all symptoms you mentioned (low heart rate, low energy), and its quite common. If not, u could have it tested first.

If u are still worried, feel free to schedule an appointment with a doctor for further check up.

A doctor.