If you are affected by a reverse gravity spell and you pass the dexterity save ( due to hanging on to a wall) how is your movement affected? On the other hand if you have nothing to hold on to and you either are floating in the air or touching the ceiling after take damage from the spell how is you movement affected?
To be clear it's a Reflex save, not a Dexterity check. Other than gravity pulling on you differently your movement is not effected. I'd probably say if when the spell hits you 'fall' to the ceiling you are likely prone (just as if you fell from a height normally and hit the ground). Once you get up you would move normally on the surface of the ceiling ... perhaps falling again if you moved out of the area without due caution. The area is not visible (and can be shaped by the caster) unless something about the environment made the area obvious (puddles on the 'floor' all around the area of puddles on the 'ceiling' for example).
Does that answer your question?
If there's nothing to hold onto, you don't get a Reflex save at all--you fall.
If there is something to hold onto and you pass your Reflex save, you're now hanging from the ceiling and can (or cannot) move in the same fashion as someone attempting to move along the ceiling of a normal-gravity area. Spider climb would be useful.