NPC starts shaking when switching from Follow AI to Wander AI

I'm working on a project where animals will wander randomly usually, but if they like the player enough, they will follow him when nearby. Currently, it's just a boolean I can switch in the inspector, when the boolean follow is true, it follows the player, else it wanders randomly. Both of these work fine on their own. The problem happens when I deactivate the follow boolean, so that it will go back to wander mode. When the boolean is flipped, the animal starts spazzing out, pointing upwards and shaking wildly, and also occasionally taking off like a rocketship. (Which, frankly, is hilarious)

Oh it might be important to mention moving is handled with the character controller component.

Here's my code for the AnimalAI script (Apologies if it's ugly, I'm new to scripting in Unity):

 using UnityEngine;
 using System.Collections;
 
 [RequireComponent(typeof(CharacterController))]
 public class AnimalAI : MonoBehaviour {
 
     //variables for speed, how much the NPC can turn, and how quickly
     public float speed = 10f, maxFaceChange = 60f, dirChangeInterval = 1f;
     public bool follow = false, fear = false;    //Whether or not the aminal loves you enough to follow you, or is currently terrified of being slaughtered
     public GameObject playerObj;        //Variable to hold the player object
     public TruckAI truck;
     Transform tf;                        //Variable to hold the Transform component
     CharacterController controller;        //Variable to hold the CharacterController component
     float startFace;                    //The start direction
     float i = 75f;
     bool willMove = true;                //Boolean to see if the animal will move this interval
     Vector3 targetRotate, toPlayer;        //Where the aminal will soon be facing, vector towards player
 
     void Awake(){
         controller = GetComponent <CharacterController> ();            //Get character controller
         tf = GetComponent<Transform> ();                            //get Transform
         startFace = Random.Range (0, 360);                            //Generate new direction to face, angle from 0 to 360
         transform.eulerAngles = new Vector3(0, startFace, 0);        //Convert to vector
             
         StartCoroutine(NewFacing());
     }
 
     // Use this for initialization
     void Start () {    
 
     }
     
     // Update is called once per frame
     void Update () {
         if (truck.parked) {        //Checks if the truck has arrived and therefore if it should be terrified
             fear = true;
         }
         else{
             fear = false;
         }
 
         if (follow && !fear) {
             //FOLLOWING CODE
             if(Vector3.Distance(tf.position, playerObj.transform.position) > 2){
                 tf.LookAt (playerObj.transform);
                 var forward = tf.TransformDirection(Vector3.forward);    //Gets forward direct
                 if (willMove){
                     controller.SimpleMove(forward * speed/3);                    //Moves in forward direction
                 }
             }
         }
         if (fear) {
             //RUNNING CODE
             Vector3 direction = tf.position - playerObj.transform.position;
             tf.rotation = Quaternion.LookRotation(direction);
             Vector3 forward = tf.TransformDirection (Vector3.forward);
                 controller.SimpleMove(forward * speed);                    //Moves in forward direction
         }
         else if (!follow && !fear){
             //RANDOMLY WANDERING CODE
             tf.eulerAngles = Vector3.Slerp(tf.eulerAngles, targetRotate, Time.deltaTime * dirChangeInterval);
                 //Turns aminal to face the correct way
             var forward = tf.TransformDirection(Vector3.forward);        //Gets forward direct
             if (willMove){
                 controller.SimpleMove(forward * speed);                            //Moves in forward direction
             }
         }
     }
 
     IEnumerator NewFacing(){
         while (true) {
             i = Random.Range (1f,101f);                //generate random number
             Debug.Log (startFace);
             if ( i > 50 || fear || follow) {        //If the random number is greater than 50, it'll move
                 willMove = true;
             }
             else {                                    //Else it won't
                 willMove = false;
             }
             NewFacingRoutine();
             yield return new WaitForSeconds(dirChangeInterval);        //Wait for specified intervals
         }
     }
     
     void NewFacingRoutine(){
         if (follow && !fear) {
             //Following
 
         }
         else if (!follow && !fear){
             //So, if it's just wandering
             var floor = Mathf.Clamp(startFace - maxFaceChange, 0, 360);        //Max rotate in one direction
             var ceil  = Mathf.Clamp(startFace + maxFaceChange, 0, 360);        //Max rotate in the other
             startFace = Random.Range(floor, ceil);                            //Generate random angle between min and max
             targetRotate = new Vector3(0, startFace, 0);                    //Set target to that
         }
 
     }
 
     void OnControllerColliderHit ( ControllerColliderHit hit ) {
         
         if (hit.collider.gameObject.tag == "Wall" && !fear){
 
             // Set the altered rotation back
             tf.rotation = Quaternion.AngleAxis(180, tf.up) * tf.rotation;    //Flip animal
             startFace += 180;            //These lines fix the facing direction value
             if(startFace > 360){
                 startFace -= 360;
             }
             NewFacingRoutine();            //Immediately makes a new heading so it doesn't try to turn back into the wall
         }
     }
 }