re:
Could you possibly have unintentionally enabled "Do Not Disturb" mode? Quick check: click the on/off switch on the side of your device to allow the screen to light up. Look in the top right corner of your device near the battery indicator. Do you see a crescent moon shaped icon? If so, simply swipe up from the bottom of the screen to reveal the shortcuts and toggle off the icon with the same image. Do Not Disturb, in case you're unfamiliar, is a very handy feature you can enable and disable as needed for when you don't want calls or notifications. If you are using your device however (screen on), then it still notifies you because you are using the device. Hope this helps.