If you have access to an external drive as big or bigger than the laptop drive, boot SystemRescueCD and ddrescue it as a backup, just to be safe. I personally haven't had it actually wipe a drive, basically it's saying switching might render it unbootable if the right drivers aren't in place.

I always back up first just to be safe though, worst case I waste a little time.

My acer laptop did the exact same thing for unknown reasons. When I switched it back to AHCI Arch (btw) booted again but windows broke and I managed to fix it with a Windows live usb. I think I had to use bcdboot and generate a new bootloader.

The last time I remember hearing of AHCI was when SATA was still new and IDE (or ATA) was king.