Sleep not recording for CFS sufferer

[SleepCFS]

My Ionic accurately records my sleep and that of all family members except for my son who has ME/CFS. It records his heart beat accurately but will not register any sleep for him when he wears it. Why? He does get sleep throughout the night but always wakes unrefreshed and in pain. If the sleep app records his heart beat shouldnt it also register him sleeping? How does the movement register work? does anyone else have a total non record of sleep activity which is not the fitbit's fault?

[SilviaFitbit]

@SleepCFS A warm welcome to the Community. Thanks for getting in touch about this. 

I appreciate the details mentioned. 

Fitbit estimates your sleep stages using a combination of your movement and heart-rate patterns. When you haven’t moved for about an hour, your tracker or watch assumes that you’re asleep. Additional data—such as the length of time your movements are indicative of sleep behavior (such as rolling over, etc.)—help confirm that you’re asleep. While you’re sleeping, your device tracks the beat-to-beat changes in your heart rate, known as heart rate variability (HRV), which fluctuate as you transition between light sleep, deep sleep, and REM sleep stages. When you sync your device in the morning, we use your movement and heart rate patterns to estimate your sleep cycles from the previous night.

If the Fitbit is having issues getting a consistent heart-rate reading or it's being wore too loosely, this could be the reason why it's not tracking sleep. For best results, your son needs to wear his device higher on his wrist (about 2-3 finger widths above your wrist bone). The band should feel secure but not too tight. 

Learn more about it by checking these articles: How do I track my sleep with my Fitbit device?  What should I know about Fitbit sleep stages? 

I'll be around if you have any additional