Oh wow that's crazy

First couple things that come to mind

1) wake locks

But I don't see that being a possibility otherwise it would show in the graph of its decline

However it wouldn't hurt to grab better battery stats if your curious about it

2) battery going bad

This sounds more logical to me, have you thought to try out a different battery to see if it does the same thing?

 

I've seen this issue with beautiful widgets (some settings) and with Waze (some settings). Turn off all push notifications in every app and then turn off sync. Also, some apps have manual download of data. Turn that off too. The problem should not exist now. You can begin testing app per app... Let us know what you find.

 

That is a classic SOD (screen of death). Mine has done that a few times. If you don't catch it, it just drains the battery in no time. Not much to do about it..just have to live with it and hope you catch it in time before the battery is totally dead. Bad news if it happens overnight and you have an alarm set to wake up. Rare but it happens