Sleep feature - Time in bed

[reserves]

Might be obvious but what is this stat and how is it measured?

My data is showing In bed for 1 hour but asleep for 7 hours, despite being in bed the whole time.

How is the watch supposed to know if I’m in bed or asleep on the sofa??

 

[reserves]

Ahh, do I have to manually tell the phone I’m going to bed??