@Littledigby: If you take off your watch at night, then I recommend toggling off Bluetooth on your phone (Settings > Connections > Bluetooth > Off, or swipe from the top of the screen to the bottom and tap the Bluetooth symbol so it greys out). Now you're disconnected from your watch, the alarm sound/vibration should come through your phone as normal. You can also head into the Wearables app, check the Apps list and toggle off the Clock app.
It is also worth double checking your Do not disturb settings via Settings > Notifications > Do not disturb > Exceptions > Make sure that Alarms is toggled on. If you head to the Clock app > Alarms > Tap the 3 dots in the top right > Settings, you can also toggle on 'Vibrate for alarms and timers' for when your phone is set to Vibrate or Mute.
