Lockscreen switching on by itself

[Tushar Thakur]

Last night I saw that the phone's screen was lit, so I pressed the lock button and it went off. After some time, again the same thing. I wasn't sure whats causing it, so I just placed the screen facing downwards and went back to sleep. By the morning the battery was drained.
Has anyone else faced anything like this?

 

[TankWart]

This happens to me when I connect my phone to a charger that is NOT connected to power supply.