Simply saying "up" or "down" might be confusing anytime you're describing people in different positions, e.g. when describing movements made by gymnasts.
I.e. If you're standing normally, your head is above your heart. When doing a handstand, your head is below your heart, but whether standing on your feet or on your hands, your head is always superior to your heart because anatomical terms are always used with reference to the anatomical position: standing upright, arms to the side, palms facing forward, etc.
Some terms are used to facilitate comparison between species, such as cranial/caudal. In a human, cranial is upwards, but in a fish, it's forwards. Since the comparable structures are oriented differently, it might be tricky to simply refer to some structure as facing "upwards", since "upwards" means different things in different species.
