Phone Dying Overnight Despite Being at 80%

Over the summer I charge my phone during the day and go to sleep with my phone being at 70, 30, 50, 26, it really doesn’t matter, I always wake up and my phone is still alive. School started back up for me (yes I’m in school still) and I started charging my phone every night so I would have it fully charged for the day. I’ve done this maybe the past 4 days because over the weekend I didn’t need to (it was fine over the weekend). But, unlike all those other times, when I woke up my phone was completely dead. I went to sleep with it at 76%?? Checked my battery usage and nothing was used during those hours, my phone was slept. This makes no sense to me and my only explanations are that my phone had gotten used to being charged to 100% so it lost rapidly (unlikely i did it 3 times last week and it was fine). Or, the thunderstorm took out my service provider and that somehow wacked up my battery 🤷‍♂️. Really confused what happened as I only lose a maximum of 16% per night and my phone, even if I leave it on, only drops maybe 50% overnight. I would appreciate some insight here and maybe a few suggestions, thank you!