Mine does this too! He stares into space and just goes a bit floppy and then comes around and shakes like he's just got out of the bath.

Guess dogs are all different, mine has some bizarre fit/absences where he like trots around the room, you know like a dressage horse? Not a clue what causes it, and not a single vet we've ever seen has seen anything like that before.

Mine's daft as a brush anyway, he lets me dress him up and outfits and then gets in a mood when I take them off... he's convinced he's a person really.