Run coroutine only when player stays inside collider?

I'm working on a survival game right now and I have a line of code in my EnemyController.cs script that changes the variable "isAttacking" from true to false after a delay (through "yield return WaitForSeconds"). For some reason, as soo n as I run into the object, my health drops all the way to 0. Any ideas?

EnemyController.cs

 void OnTriggerStay (Collider col)
     {
         if (col.gameObject.tag == tag && !isAttacking) {
             StartCoroutine ("Attack");
             isAttacking = true;
         }
     }
 
     void OnTriggerExit (Collider col)
     {
         StopCoroutine ("Attack");
     }
 
     IEnumerator Attack ()
     {
         yield return new WaitForSeconds (attackDelay);
         isAttacking = false;
     }

Player.cs

 void OnTriggerEnter (Collider col)
     {
         if (col.gameObject.tag == damageTag && !dead) {
             canTakeDamage = true;
 
             EnemyController enemCont = col.gameObject.GetComponent<EnemyController> ();
             health -= enemCont.damage;
 
             Debug.Log (canTakeDamage + ", " + health + ", [PLAYER HIT ONCE; COROUTINE SHOULD ONLY RUN ONCE]");
         }
     }
 
     void OnTriggerStay (Collider col)
     {
         if (col.gameObject.tag == damageTag && !dead) {
             canTakeDamage = true;
 
             EnemyController enemCont = col.gameObject.GetComponent<EnemyController> ();
 
             if (enemCont.isAttacking) {
                 health -= enemCont.damage;
             }
 
             Debug.Log (canTakeDamage + ", " + health + ", [PLAYER STAYED; RUNNING COROUTINE]");
         }
     }
 
     void OnTriggerExit (Collider col)
     {
         canTakeDamage = false;
         if (!dead) {
             Debug.Log (canTakeDamage + ", " + health + ", [PLAYER LEFT; COROUTINE STOPPED]");
         }
     }