Apple Watch only shows red lightning bolt and time

I found this article on Apple's Website! Seems as though your watch is in Power Reserve Mode!

Check your battery and charge your Apple Watch - Apple Support

"To charge your Apple Watch:

1. Plug the Apple Magnetic Charging Cable, Apple Watch Magnetic Charging Case, or Apple Watch Magnetic Charging Dock into its USB power adapter.
2. Plug the adapter into a power outlet. You can also plug the charging cable into a USB port.
3. Position the back of your Apple Watch on the charger. The charger's magnets align your Apple Watch, and you'll see a charging symbol on the watch face.
4. Give your Apple Watch time to charge. While your device is charging, you'll see on the screen of your Apple Watch."

Hi

Your watch has entered into Power Reserve mode, as the battery charge has fallen to a low level.

To restart your watch, press and hold the Side button (the lower button) until you see the Apple logo.

You may need to charge your watch first (allow up to 2.5 hours for a full charge):

Check your battery and charge your Apple Watch - Apple Support