Any chance it's an idiomatic expression? Something like going to sleep (nous commanderons l'horizontale, or we'll take the horizontal position, aka lying down in bed) and getting up (... la vertical, or standing up)?
Greatly depends on the context where it's used, and someone with a wee bit more familiarity than I (Luvian?) could clarify whether it is an idiomatic expression, or just an idiotic expression from me
