Basically I'm asking if you cloned your nand onto a partition of your SD card for CFW, or is your CFW running of the nand on your Switch.
In any case, if you didn't understand what I said, and don't recall doing any steps like that, I imagine you're not using emunand or emuMMC.
Anyhow, if you Switch suddenly doesn't boot when all the settings and firmware hasn't changed, it might be time for you to get a new SD card.