a ball moving down a wall with no gravity??

im trying to make a ball bounce off a wall but with no y axis involved. so it just stays on a certain height. but when i get the ball moving and it collides with the wall. it rolls downwards. ( i have yet to figure out how to make it go in the opposite direction yet)
if it were to roll on the x or z axis due to its sphere shape, thats understandable, but why is it rolling downwards? is it also because of its shape?
i am using rigidbody for this sphere and have disable gravity already.
i am ASSUMING i can just stop this by checking if it is touching a wall and just make it stop moving but at the same time i just want to know why this is happening.

 

Find the Rigidbody in the inspector. Then expand Constraints and here you have options to freeze a specific axis. From what I understand you are interested in selecting Freeze Position Y.

Edit:
If that's not the case, it's best to post a demo on https://play.unity.com/. How to publish you have here https://learn.unity.com/tutorial/creating-and-publishing-webgl-builds#.

Edit 2:

You must notice that Unity simulates some physical properties. Even if you turn off gravity, the object still has velocity so it can direct it along a different axis. So the object isn't falling, it's just speeding along surface Y.