Ever grabbed your switch and one of the Joy-Cons were not being detected while being attached to the Switch? Well I have.

I woke up, checked to see if my Switch Review had published, and decided to grab my Switch and relax for a bit. But Nintendo obviously had other plans for me. And I was shown this screen when I unlocked my Switch...

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Notice how the Right Joy-Con is greyed out in the bottom left of the screen? Well that's bad since it was attached to the Switch, and should be white.

So after crawling the Nintendo's Self-Help documentation and keeping seeing "Call this US number, and we will replace it", which is a death sentence to my saves, since Nintendo has no Cloud save support! So how did I fix it, and keep my saves?

Well firstly I left the Switch with both Joy-Cons on the charger for half an hour, mainly since the Joy-Cons stop charging when the Switch goes to sleep, for obvious reasons.
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I pressed and held the Sync button for 15 seconds, which is not something Nintendo ever mentions, on the affected Joy-Con, it will restart and the LEDs lit up and started scrolling again trying to connect to the Switch.
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And Voila it works.