Why is my apple watch lighting up at night

Just recently, my Apple watch ultra started having the green lights on the bottom come on when the watch is not on my arm or unlocked. I recently started to notice it when my alarm on my phone would go off in the morning, then right afterward, the green lights on the watch will come on while its sitting on the nightstand. Its not charging when this happens. I also noticed when I first put it on in the mornings, I go to immediately check my heart rate and it shows that the last heart rate measure was two hours before I even put on the watch. And the watch's battery is draining really fast. I can't make it through the day on a full charge. the WatchOS version is 9.5.1 (20T570)