Timer Spawn Freezing Unity C#

Whenever I run the code to spawn my asteroids after a certain amount of seconds at predefined locations, Unity always freezes on me! I don't know what is wrong with the code, there is no errors, it just waits for the 4 seconds and then freezes. Help!

 using UnityEngine;
 using System.Collections;
 
 public class Spawner : MonoBehaviour {
 
     private PlayerLevel level;
     public float timer = 1f;
     public float secondsToWait= 4f;
     public float totalSeconds;
 
     public Transform[] spawn;
     public GameObject asteriod;
 
     void Start () {
         level = GameObject.FindGameObjectWithTag ("Player").GetComponent<PlayerLevel> ();
     }
     
     void Update (){
         int spawnNumber = Random.Range (0, 1);
             if (totalSeconds <= secondsToWait) {
                 if (timer > 0) {
                     timer -= Time.deltaTime;
                 } 
                 else if (timer <= 0) {
                     totalSeconds++;
                     timer = 1f;
                 while (level.level >= 1) {
                     if (totalSeconds == 4f) { 
                         Instantiate (asteriod, spawn [spawnNumber].position, spawn [spawnNumber].rotation);
                         secondsToWait = 4f;
                         }
                     }
                 while (level.level >= 5) {
                     if (totalSeconds == 2f) { 
                         Instantiate (asteriod, spawn [spawnNumber].position, spawn [spawnNumber].rotation);
                         secondsToWait = 2f;
                         }
                     }
                 while (level.level >= 10) {
                     if (totalSeconds == 1f) { 
                         Instantiate (asteriod, spawn [spawnNumber].position, spawn [spawnNumber].rotation);
                         secondsToWait = 1f;
                         }
                     }
             while (level.level >= 15) {
                 if (totalSeconds == 0.5f) { 
                     Instantiate (asteriod, spawn [spawnNumber].position, spawn [spawnNumber].rotation);
                     secondsToWait = 0.5f;
                     }
                 }
             }
         }
     }
 }

Thanks in Advance,

Nick