If you are on a mount and it is knocked prone, do you automatically get knocked prone too?
To set the scene, I am mounted on my Warhorse when an evil NPC casts Earthquake below where we stand. My Warhorse makes a saving throw but fails and is knocked prone.
Does this mean that I too would automatically be knocked prone? Would I need to make a separate saving throw against the spell? Or, do I need to do an Acrobatics check for instance to see if I can land on my feet?
I would appreciate responses with RAW or RAF.