Problem with locking rotation

 yRotation = transform.rotation.y;
 transform.rotation = Quaternion.Euler(0,yRotation,0);

This locks rotation on all axes for some reason, including Y.

I need to be able to lock and unlock the rotation though. Here is the full script:

 using UnityEngine;
 using System.Collections;
 
 public class playerMovement : MonoBehaviour 
 {
     float horizontalAxis;
     float verticalAxis;
     float deltaTime;
     int speed;
     Quaternion rotation;
     int mouseSensitivity;
     int pitchSpeed;
     public string moveMode;
     int gravityFactor;
     int jumpHeight;
     CharacterController controller;
     Vector3 moveVector;
     public float yRotation;
     
     void Start()
     {
         speed = 1000;
         mouseSensitivity = 300;
         Screen.showCursor = false;
         pitchSpeed = 30;
         moveMode = "flight";
         gravityFactor = 30;
         jumpHeight = 30;
         controller = GetComponent<CharacterController>();
     }
     
     void Update()
     {
         if (moveMode == "flight")
         {
             deltaTime = Time.deltaTime;
             horizontalAxis = Input.GetAxis("Horizontal");
             verticalAxis = Input.GetAxis("Vertical");
             
             if (verticalAxis != 0)
                 rigidbody.AddRelativeForce(0,0,verticalAxis * deltaTime * speed);
             
             if (horizontalAxis != 0)
                 transform.Rotate(0,0,-horizontalAxis * deltaTime * pitchSpeed);
             
             if (Input.GetKey(KeyCode.Space))
                 rigidbody.AddRelativeForce(0,1 * speed * deltaTime,0);
             
             if (Input.GetKey(KeyCode.LeftShift))
                 rigidbody.AddRelativeForce(0,-1 * speed * deltaTime,0);
             
             if (Input.GetAxis("Mouse Y") != 0)
                 transform.Rotate(-Input.GetAxis("Mouse Y") * deltaTime * mouseSensitivity,0,0);
                 
             if (Input.GetAxis("Mouse X") != 0)
                 transform.Rotate(0,Input.GetAxis("Mouse X") * deltaTime * mouseSensitivity,0);
             
             rigidbody.angularVelocity = new Vector3(0,0,0);
         }
         else
         {        
             yRotation = transform.rotation.y;
             transform.rotation = Quaternion.Euler(0,yRotation,0);
         }
     }
 }