You are accessing isDead like a static variable. Use Getcomponent from gameobject which holds that playerscript instance or set is isDead static, which i don’t suggest as its player, and is not statically living for the whole software life time.
using UnityEngine;
using System.Collections;
public class PlayerHealth : MonoBehaviour {
public static PlayerHealth current;
public bool isDead;
void Start ()
{
current = this;
}
}
You can now access isDead wherever you like calling: