Dead phone, only vibrations

My phone was normal throughout the day and when I woke up the screen a few minutes back, the phone was literally dead.
I pressed and hold the power button for 20s and all I got was the vibration. Tried both the buttons combination of power + volume up/ down and all I get was vibration only. I plugged the phone into the charger and nothing came on the screen of the phone as well.

Any ideas? Phone was at 70%+ when this happen