i probably can explain
ok for the first it's upside up cuz the upside is facing up and upside down is the up side is facing down
and for your second question 1 d is going two directions but 2d is 4 directions but 3d is 6 direction but what are the next ones well the theory says that 4d is a 3d dimension but with a 2d or 1d creature on it and for beyond D it's believed that it's beyond our current understanding