Acting as though the laptop Fn key is pressed

The Fn key is generally handled via the ACPI BIOS rather than directly by the operating system, so there is unlikely to be anything that Ubuntu itself can do.

One possibility is that you've turned on the NumLock, which might cause those keys to default to numbers instead of letters. Hitting the key (or key combo: on my laptop Number Lock is toggled by the Fn+ScrLk key combo) again should set things back to normal.

If that doesn't work, restarting the system will probably return it to the default state.

Had the same issue with DELL Inspiron 15 5000 Series :

Solution is to press Fn+Esc.

On samsung laptop, there are "Fn Lock" button on right-top of the keyboard so that it fixed.