my iphone 6s has a dark screen and the circle is spinning

[judy-worley]

How do i restart

 

[Tartarus]

Hold down the power button and the volume down button at the same time for 10 seconds and release them. Your iPhone will restart.

 

[trw1602]

This happens to me when I update over 10 apps at the same time, only periodically. Wonder what causes this?