Here is the rundown of my instance of this problem:
-Went to bed and left my iPhone 5 on with a Bluetooth alarm app called AirAlarm2 on.
-Woke up to my phone at 1% power despite it having been plugged into the wall all night. It wasn't the outlet or the app (I have used it many times before without this issue).
-I plugged the phone into a different outlet and closed all my applications and changed the phone to low-power mode. It started charging.
-While in the power settings menu, I noticed that the messages app used 66% of my battery in the last 24 hours, which seemed very abnormal, so I went to open the messages app only to find that the phone had stopped operating; the messages app icon stayed darkened as if it was frozen in a pressed state, but the app didn't open. When clicking the icon again, it depressed and looked normal again. Still, the messages app didn't open. The phone reacted to sliding the home window left and right, but none of the other apps responded either, and all reacted in a similar way. App groupings didn't expand, either.
-I left the phone for a minute and the screen locked. At this point, I arrived at an issue I had had three times before, within the previous couple of days. The screen remained black, no matter what button was pressed or held, with the exception of both the home and lock buttons, which was my only way of giving my phone a hard reset/temporary fix. Despite it's unresponsiveness, I could tell the phone was still on because muting and then un-muting the sound resulted in a vibration, and unplugging then plugging my phone in resulted in the charging sound. Also, while in this state, I tried holding the lock button to turn it off and after a few seconds of holding it, I swiped my finger from left to right at the top of the screen as if it still displayed the power-down slide-bar, but nothing happened (I could tell it was still on by the same means in the last sentence).
-It seems as though it is an issue with the software, and this only started happening after I updated to iOS 10.3.1.