Instant Game Over - Game Broken!

using UnityEngine;
using System.Collections;

public class PlayerHealth : MonoBehaviour {

    public bool alive;

    [SerializeField]
    private GameObject pickupPrefab;

    // Use this for initialization
    void Start () {
        alive = true;
    }

    void OnTriggerEnter(Collider other) {
        if (other.CompareTag("Enemy") && alive == true) {
            alive = false;

            Instantiate(pickupPrefab, transform.position, Quaternion.identity);
        }
    }
}

using UnityEngine;
using UnityEngine.UI;
using System.Collections;

public class GameState : MonoBehaviour {

    [SerializeField]
    private Text gameStateText;
    [SerializeField]
    private GameObject player;
    [SerializeField]
    private BirdMovement birdMovement;
    [SerializeField]
    private FollowCamera followCamera;

    private PlayerMovement playerMovement;
    private PlayerHealth playerHealth;

    private bool gameStarted = false;

    private float restartDelay = 3f;
    private float restartTimer;

    // Use this for initialization
    void Start () {
        Cursor.visible = false;

        playerMovement = player.GetComponent<PlayerMovement>();
        playerHealth = player.GetComponent<PlayerHealth>();

        playerMovement.enabled = false;
        birdMovement.enabled = false;
        followCamera.enabled = false;
    }

    // Update is called once per frame
    void Update () {
        if (gameStarted == false && Input.GetKeyUp(KeyCode.Space)) {
            StartGame();
        }

        if (gameStarted == true && playerHealth.alive == false) {
            EndGame();

            restartTimer = restartTimer + Time.deltaTime;
            if (restartTimer >= restartDelay) {
                Application.LoadLevel(Application.loadedLevel);
            }
        }
    }

    private void StartGame() {
        gameStarted = true;

        gameStateText.color = Color.clear;

        player.SetActive(true);
        playerMovement.enabled = true;
        birdMovement.enabled = true;
        followCamera.enabled = true;
    }

    private void EndGame() {
        gameStarted = false;

        gameStateText.color = Color.white;
        gameStateText.text = "Game Over!";

        player.SetActive(false);
    }
}