Sleeping with mouth open maybe?

This morning my temp dropped below my cover line (97.29). I took one look at it and thought, that can't be, so I tried again and it came back 97.59. Still a dip from yesterday, but nowhere near as extreme. I recorded the 97.29, but I feel like that first temp was way off. Temp were taken within a minute of each other, so I didn't think there should have been a big difference. Thoughts?