Guess what? I also experienced this problem yesterday! My phone got extremely hot (not warm!) and I started worrying like you do. So, like most of you, I took out the battery, rebooted, and did that several times and the battery was still burning!
Luckily, I found a free app called Watchdog Lite. It's a task manager that shows the CPU usage. So, I downloaded it, and found out there is this Bloomberg app that I recently updated two days ago was running my CPU at over 55%!! At first, I thought it was normal (even Watchdog kept on prompting me) because I didn't have a clue what is a "normal" CPU usage for an app -- especially when I have Bloomberg installed on my Galaxy Note for months without problem!
But then, this morning, the phone got hot as hell again, and the battery dropped 5% within 5-10 mins! So, I fired up Watchdog, found out all other Apps are only using 0.x% whilst Bloomberg was still over 50%, I knew the culprit was that Bloomberg recent update.
So, I uninstalled that crap, and my phone is now back to normal!
Hope this helps!