Hmm that doesn't sound right..
First try Booting into safe mode and see if the same, if not and it's cool, one of your apps is eating processes. If still the same you can try
a backup using Xperia Companion followed by a software repair using Xperia Companion
That should clear up any rogue code that's causing it.
If it still is getting hot
Contact your Local support for a device assessment.
Note that after a repair installation, the devices do get hot whilst installing and restoring apps and settings.
