Some smart watches may track time while charging, or off your wrist, as "Sedentary time". Therefore, if you did not wear your watch to sleep, you may see a very large number of sedentary minutes in the morning. Wearing your smart watch to sleep will help keep your sedentary number accurate - as well as giving you insights on your sleep!
If you did wear your watch to sleep and are still seeing an abnormally high Sedentary number in the morning, check that your sleep was captured properly. You can do this by syncing your Fitbit Device with the Fitbit App or by checking your Apple Health Sleep data. After syncing your device, refresh your Sensable Health Application, and your Sedentary Minutes should update to reflect an accurate Sedentary Time.