Welcome to Android Central! Has this behavior continued? The battery might be failing. Take it out, lay it flat on a table, and try to spin it. If it spins freely, it's bulging in the middle, which is a bad sign--try a new battery.
A corrupt SD card can also cause behavior like this. Unmount the card (in Settings>Storage), remove it, and reboot. You could try a different SD card, as long as you know that card is good.
Screenshots of the battery stats would be good, if this happens again.