Goto support on your device to test.
- the support app
- settings->system->about phone
and run tests
Other method to verify is reboot in Safe Mode (switch off and long press on the Power Off choice)
See if the problem persists.
If it does you could try to backup your data with Xperia Companion and do a software repair with Xperia Companion.
If all fails then goto the support app and use it to take up contact with Sony Support.
Hope something will work out for you.
