Usually "idiopathic" anxiety is caused by inflammation (small intestine - low bile flow and fungal/bacterial overgrowth) and blood Sugar swings - hypoglycemia.
Then adrenaline is produced in order to bring the blood Sugar level up. That is why one may be is vicious circle of adrenaline release.
In my opinion adrenal fatigue does not exist and it is adrenal dysfunction or adrenal dysregulation if you want.