Rotate back to original x rotation

Hello! I have a first person controller that tumbles while freefalling then when it is a certain distance above the ground it rotates back to its original(standing) rotation. The problem I have is that it rotates it back to its x y and z rotations, where I only want it to be back at its original x rotation (it can be facing any direction, think like a cat landing on its feet). The code I have is this:

 public Quaternion origRot;
 ........
 origRot = transform.rotation;
 ........
 transform.rotation = Quaternion.Lerp(transform.rotation,origRot,1.0f * Time.deltaTime);

The periods are filler because I took out a lot of unrelated code, but what can I do to make this work correctly? Thank you ahead of time!