Unfortunately you are talking nonsense. I see people on a regular basis with zero immune system, literally, due to chemo or other immunosuppressive therapies and they are sick constantly. Diabetics similarly.
I cant speak for your own case, but othetwise you are way of the mark.
By the way many people with poor metabolisms have an abundance of energy courtesy of cortisol and adrenaline. Its not a good thing though.
Well it's not nonsense.
It's common in eating disorder states to never ever get sick, only for the immune system to kick in during recovery and lots of symptoms to finally present.
Where each individual is at is up for debate, but it's certainly a good question to be asking.