Stamina Script causes Crashing?

I've been trying to implement a Stamina system to my Sprint Script (JavaScript) but for some reason it causes my game to crash. I've pinpointed two instances that causes it to crash: 1) In the following lines of code:

while (stamina < 100)//if stamina is less than 100%
	{
		while (walking)//when walking
		{
			stamina = stamina + 0.25 * Time.deltaTime;//stamina increases at 1/4th the rate it depletes
		}
	}

Whenever I try to sprint, Unity crashes. 2) If the block above is commented out, in the following lines of code:

    switch (stamina)
	{
		case 0://if stamina fully depletes
		recover = true;//recovery mode is enabled
		break;
	}
	if (recover)//if in recovery mode
	{
		while (stamina < 25)//while stamina is less than 25%
		{
			speed = walkSpd;//walking speed is the max speed
			if (stamina >= 25)//if stamina is equal to or greater than 25%
			{
				recover = false;//recovery mode is disabled
			}
		}
	}

Unity crashes when Stamina reaches zero. Here is my entire script:

#pragma strict

private var walkSpd : float = 4; //Walking speed value
private var jogSpd : float = 6; //Jogging speed value

private var charMotor : CharacterMotor;
private var charController : CharacterController;
var stamina : int;
private var recover : boolean;
private var walking : boolean;

function Start () 
{
	charMotor = GetComponent(CharacterMotor);
	charController = GetComponent(CharacterController);
	stamina = 100;
	recover = false;
	walking = true;
}

function Update () 
{
	var speed = walkSpd;//sets default speed to walking speed
	
	if (charController.isGrounded && Input.GetKey(KeyCode.LeftShift) || charController.isGrounded && Input.GetKey(KeyCode.RightShift))
	{	//if the player's character is on the ground AND he/she is pressing a SHIFT key
			speed = jogSpd; //the player moves at jogging speed
			stamina = stamina - 1 * Time.deltaTime; //stamina decreases over time
			walking = false; //the player is not walking
	}
	else //if the player is NOT on the ground AND holding a SHIFT key
	{
		/*speed = walkSpd;*/ //the player's speed is walking speed
		walking = true; //the player is walking
	}
	switch (stamina)
	{
		case 0://if stamina fully depletes
		recover = true;//recovery mode is enabled
		break;
	}
	if (recover)//if in recovery mode
	{
		while (stamina < 25)//while stamina is less than 25%
		{
			speed = walkSpd;//walking speed is the max speed
			if (stamina >= 25)//if stamina is equal to or greater than 25%
			{
				recover = false;//recovery mode is disabled
			}
		}
	}
	while (stamina < 100)//if stamina is less than 100%
	{
		while (walking)//when walking
		{
			stamina = stamina + 0.25 * Time.deltaTime;//stamina increases at 1/4th the rate it depletes
		}
	}
	charMotor.movement.maxForwardSpeed =  speed; //Setting new speed variable under appropriate conditions
}

What am I doing wrong?