Hi China_Sprog, welcome to the Sony Forums 
When you import with PMB you convert the camera's original files to .mts format. Unfortunately PMB won't recognise .mts files for import (only the camera's native files) hence you won't see them when you try to re-import from your external drive.
One solution would be to get hold of some software which will convert the files to a format that PMB will recognise, such as .avi or mp4.
In future, if you can import to an external drive while you're on holiday, maybe you could make an exact copy of the data on the card as a backup instead, which will then be visible to PMB on your home PC, or at least make sure the backup is made on a laptop which you can later use to edit, to avoid having to do intermediate conversions.
Cheers
Mick