Problem with rotating a rigidbody

Hello!

This is my first time posting here, sorry for any mistakes I make.

I have a problem with my C# script. I'm no programmer, unfortunately, I only know the basics I learned myself. I wrote a simple script to move my guy about and it works great, he walks, he runs, the turning is smooth... until I try to move him back. On both gamepad analog stick and the WASD keys as soon as I try to rotate and move the character towards me, he flips upside-down and falls through the floor. I have looked online and re-wrote the script a dozen times but it only made it worse.

Edit: Just wanted to clarify that my camera is old zelda-like, suspended above the character and the character moves in the direction the analog/WASDies point.

Here's the code (sorry if it didn't format properly, I've tried):

 using UnityEngine;
 using System.Collections;
 
 public class CharacterControl : MonoBehaviour {
 
     float xTilt;
     float yTilt;
 
     public Animator animator;
     public float speed = 0.0f;
     public Vector3 targetDirection;
     public Transform mcamera;
 
     // Use this for initialization
 
     void Start () {
         animator = GetComponent<Animator>();
         mcamera = GameObject.FindGameObjectWithTag("MainCamera").transform;
     }
 
     
 
 
     // Update is called once per frame
     void Update () {
     
     }
 
     void FixedUpdate (){
 
         xTilt = Input.GetAxis("Horizontal");
         yTilt = Input.GetAxis("Vertical");
     
     //rotation maths
             if (xTilt != 0 || yTilt != 0){
 
             Vector3 currentDirection = rigidbody.transform.forward;
             targetDirection = (xTilt * rigidbody.transform.right + yTilt * rigidbody.transform.forward.normalized);
 
 
             Debug.DrawRay(rigidbody.transform.position, currentDirection, Color.green, 20f);
             Debug.DrawRay(rigidbody.transform.position, targetDirection, Color.red, 15f);
 
 
             
 
             rigidbody.MoveRotation(Quaternion.FromToRotation(currentDirection, targetDirection));
             
 
             
         //animation control
             speed = targetDirection.magnitude;
             animator.SetFloat("Speed", speed);
 
 
             
         }else animator.SetFloat("Speed", 0.0f);
 
         if(Input.GetButton("Crouch")){
             animator.SetBool("Crouch", true);
         }
         else animator.SetBool("Crouch", false);
     }
 }

If anyone could tell me what am I doing wrong here, so I can learn for the future, I'd appreciate it greatly.

Thanks in advance for any help!