Apple Watch

I recently purchased an Apple Watch and linked it to my iPhone.

I have been using the sleep tracker on the watch for two weeks or so, the tracker shows two different colors for tracking time in bed and actually sleeping. The last couple of days it has only showed me time in bed and no data for sleeping. I check everything in settings and I can’t find the problem. Does anyone else have this issue? Does anyone know why this is happening and how I can fix it to show the complete data.

thank you in advance for help!