Yesterday I changed my Fitbit sleep monitor setting from "normal" to "sensitive." I got to bed last night at almost exactly the same time I went to bed Sunday night; and I got up this morning within 5 minutes of when I got up yesterday. But my Fitbit says I got 90 minutes less sleep last night. Here's Sunday night:
Here's last night:
This means either it's been overestimating my sleep, or last night it hugely underestimated it. Or, possibly, last night I just tossed and turned a lot more than usual.
I'll keep it on the "sensitive" setting for a week or so and compare it with how I feel in the morning. I definitely wanted to sleep in today, but it's also rainy and cold. More data is required.