How old is your son? Because I basically inherited this from my mom and it didn't hit me until I was 35?
If you had adrenal insufficiency when you were pregnant, there is a really good chance he is heading for it as well.
Is your son a high energy person? Is he a type-A person? Does he exercise intensely? Is he the type of person that never relaxes?
One can be in the "Adaptation Stage" of the General Adaptive Syndrom for decades...feeling better than most people, until the exhaustion happens.