Epigenetics and pre-natal conditions may be a major factor.
My mom was the oldest of 16 siblings. I’ve got over 40 cousins on that side of the family. All my uncles, aunts, nieces and nephews have the symptoms people report on this forum.
I freak them out because I’ll guess at their symptoms, asking them if they have specific symptoms like “do you have to pull over and urinate every 45-minutes while driving”.....”do you jump and answer the phone on the first ring”....”do you have an afternoon energy crash….but get a boost of energy late in the evening”.....”do you ever wake up with numb hands” ….”do you have brain fog sometimes”
The entire family is wired and tired. Never ever returning to homeostasis.
Even my relatives that have had very low stress lives have “adrenal fatigue” symptoms. ….excessive startle response, the whole nine yards. They have no reason to be wired, but they are.
Here are a few hints of how pre-natal conditions and epigenitcs affects off-spring
Prenatal cortisol exposure predicts infant cortisol response to acute stress