Wow, this is interesting. My oldest son, now 30, had this growing up (don't know if he still does). I read the posts both here and where someone left a link. High blood pressure makes the most sense to me to be the cause in his case. My son seemed to be the healthiest in all the family. When he did get sick he would just sleep all day and then be fine. He got well without much in the way of symptoms or any medicine. But he did get diagnosed with high blood pressure at age 4 when he was going through some anger. He's now on blood pressure medication because he was diagnosed at age 29 with hypertension. Hmmmm, interesting. I never even thought others were getting that symptom too!
Speaking of allergies, some of us in the family have them but he was never diagnosed with any, didn't appear to have any reactions but all my babies didn't do well with cow's milk.