I tried factory reset, software update but it didn't work... So the problem is in the hardware. I went to Sony authorised service, they made me wait for 2hrs then they said they are going to send the phone to factory within 3 days they'll call and tell the estimate then I have to pay advance... These things are not a matter but at end they said if the phone becomes dead during their process then Sony is not responsible its my own risk. So I left the place with my phone.
Now I turned off adaptive brightness and increased brightness to max so the problem doesn't occur... But its like a temporary solution...
