Sense registers sleep when I'm not wearing it

[FitbitUser1112]

Most Sunday mornings, I take my Fitbit Sense off for 2-3 hours to give my arm a rest. For the past few weeks, I have noticed that, at least a couple of times, those hours (or parts thereof) are recorded as "sleep" while, I am wide awake and working, watching TV or reading the papers. None of this occurred when I was using the Ionic or the Surge in years past.

Any reason? 

Moderator edit: updated subject for clarity.

[LokeAa · Accepted solution]

@FitbitUser1112 , the optic sensor will try to read any surface, and therefore it can give false readings. Advice is to shut down your Sense when you are giving your arm a rest.