Still fairly inexperienced, I hit the button right of the “disk” entry in the file utility, and was flabbergasted as my disk was gone. Ok, I found out soon that a restart remounts it - and understood what had happened.
Anyway, the question arises whether it is possible to remount without restart.
Thanks for the answers. And yes, I am writing about SD cards.
And I was looking for a software remount, not a hardware one.
Moreover, removing an SD card on FP5 is only possible when removing the battery. So a reboot would be necessary anyway, and a software triggered reboot would certainly be faster and easier than removing battery and SD, then reinserting SD and battery.