When my DH's son was in his twenties, he experienced symptoms that concerned him enough to seek medical care, but was told he had the flu more than once over the course of a couple of days.  He  sought emergency care at a hospital after a couple of days of being sick, thinking that what he was being told couldn't be correct.

It turned out that by the time he was seen at the emergency level and correctly diagnosed he was on the edge of a diabetic coma.   He was extremely close to dying.