Measuring heart rate when I sleep

[Tntfish222]

I injured my hip about 4 weeks ago so I had to sleep on my recliner for 3 weeks (almost horizontal). Not entirely comfortable, but I noticed my heart rate was below my RHR around 80% of the time. When I sleep in my bed, I’m lucky to get 20%. It dramatically impacts my sleep score. I have almost a year of history to consider. 

Why is this? Is it my Charge 2 watch location relative to my heart (above or below it) when I sleep? On the recliner, it’s slightly above it resting on the arm rest. In bed it’s usually slightly below my heart unless I’m on my side with my arm on a pillow.

I don’t trust this sleep number. It is frustrating though when I get a rating of 85+ on an uncomfortable recliner, and I can’t get out of the 60s in a comfy bed. Please help. 

[JohnnyRow]

Height of your wrist wouldn't affect heart rate; it does affect measured blood pressure but that's not relevant here.

For myself, I'm not so quick to call a recliner uncomfortable for sleeping.  I often spend about half the night sleeping in recliner, at least until it finally broke and I haven't gotten around to replacing yet.  In bed I sleep on my side but either hip is likely to get sore after a few hours so I have to keep rolling over.   On recliner I can sleep on my back but have my upper body half-way elevated, which is most comfortable for me.