Hey Kale,
That sounds very odd for a phone to drop in battery that much. How long was it off of the charger before it dropped that low? If you can check the battery history using the stock battery viewer in settings or via a third party app, are there any applications that are keeping your phone awake even when the screen is off? This can contribute to fast consumption of the battery. Have you downloaded any new apps recently? Uninstalling the last few apps and reinstalling slowly over the next few days can pinpoint which app it is that is causing your phone to go haywire.