You can make note of how you're feeling after a night's data in the "Quality" section of your app.
Why keep tabs on how you're feeling during the day?
The most important gauge of the quality of your sleep is how you feel during the day.
Keeping track of this will allow you to connect what kind of night you've had with how you're feeling during the day and to see how this evolves in the long-term.
When should you enter your mood?
We don't recommend any specific time but it's best to avoid rating your mood just after getting out of bed. How you feel in the morning can be influenced by which sleep stage you're in when you wake and this doesn't always reflect the overall quality of your night.