Hi. In young people low heart rate while drifting jnto sleep or asleep is normal. However if yourlow heart rate is associated with symptoms of dizziness then you need to get evaluated.
You may need other tests like
Thyroid profile and serum
electrolytes to see if everything is ok
If your heart rate is increasing proportionately to your activity then it is ok
Next Steps
Seek consultation with a doctor for proper evaluation
Health Tips
If low heart rate with dizziness persists and other tests are normal you may need further evaluation with 24 hours Holter test