Hi simor1947,
Welcome to the Apple Community.
Wondering if your Watch may not have been charging:
The battery must have at least 10 percent charge for your Apple Watch to restart.
You might want to try putting the Watch back on the charger,.
If your Apple Watch is out of power, you might need to wait a few minutes for the green lightning bolt to appear after you start charging your device.
How to Return to normal power mode after being in reserve power mode
Restart your Apple Watch—press and hold the side button until the Apple logo appears
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If you still need help:
Try Apple Support's articles to help troubleshoot:
Restart your Apple Watch - Apple Support
If your Apple Watch won't charge or it won't turn on - Apple Support
Turn on and wake Apple Watch – Apple Support
NB: Choose correct Watch OS at the top of this aricle
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More info:
Apple Watch User Guide
For everything you need to know about Apple Watch
Apple Watch User Guide – Apple Support
(NB:You can click on "Table of Contents" to see what's available.
For accurate info: hoose the Operating System of your Watch (watchOS) at the top of articles.
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For support from Apple, if needed:
Apple Watch Support online:
Apple Watch - Official Apple Support
Or
Apple phone numbers around the world
Contact Apple for support and service - Apple Support
All the best :-)