Maybe you have accidentally turned off your mobile device. If this is the case, all you have to do is to turn on your mobile device.
It is very important to update the device's operating system on time as the updates contain fixes to various bugs. If you don't receive a notification about the update, check if one is available manually.
See the don't know how to update my operating system guide if you are not sure how to check for updates manually.
Maybe the vibrator got stuck. A gentle tap on the back of the device should be enough to unstuck it.
If your device doesn't vibrate at all and its battery is removable try restarting it by removing its battery and reinserting it after 2 minutes.
If this mode is on, you won't be able to receive notifications that somebody tried to reach you. You can disable this mode via Settings:
If you don’t receive the email in the next 2 minutes please check your junk folder, and add [email protected] to your safe sender list.