Camera draining iPhone battery overnight without running in the background

I have a doubt. I charged my phone last night till the battery percent was up to 80 or so. Then when I woke up next morning, my phone got switched off without any charge. How so..? When I checked my battery status over night it showed camera used 100 percent of my battery. But my camera was not running in the background. What is happening..? I’m scared.

[Re-Titled by Moderator]

Original Title: Hacking my camera