Use the Bedside Mode
The Apple Watch can track a variety of sleep statistics, but not everyone cares about that feature or finds the information usable. If you’re more comfortable with your Apple Watch off while you sleep, you can turn it on its side to enable the Bedside Mode, which turns the Watch into a mini Alarm Clock clearly showing the date and time as well as any alarms you have enabled.
If you’re home, you can pair Bedside Mode with a compatible wireless charger, but this trick is often most useful when traveling or taking a quick nap to regain some energy.