Reboot the device.. Do you have anything like gsam installed?? You might try that. You could've had an app or apps going rogue... Using up processor cycles and causing the over heating.. Definitely reboot by holding power and volume down at the same time for about 10 Seconds.. (it will probably take a screen shot.. Just keep holding.)
Then once you install gsam.. Run the device a few days. Keep an eye on it.. (gsam will tell you the temp) and it has a feature called app sucker..it will tell you if any apps are staying awake and running for no reason.