I vote for major injury messing with your brain. (Idiocy related to youth may have been a complicating factor.)
In college I went roller skating one evening. I fell and broke my arm. I knew at once I was in pain like I’d never suffered before. But, I didn’t really believe I was badly hurt. I was so focused on getting over to where it was safe, that I almost caused a pile-up (with me on the bottom) by skating in front of fast moving skaters, but a friend who saw me fall grabbed me by the broken arm and held on to me until it was safe to cross.
Another friend got me a bag of ice, and after 15 minutes or so I tried skating again–found that my wrist hurt more when it swung. I’m not sure I believed yet that I should go to a doctor. Then I noticed a bump on my wrist, that did not appear on my other wrist. I pointed this out to others, one of whom said “Dave, drive her to the hospital at once, do not pass go, do not collect $200” (OK, not a direct quote). I persuaded people that I should go back to campus and pick up my insurance card, and that really, i only needed one friend to drive me to the hospital. she took me, they processed me, they asked if I could possibly be pregnant, they x-rayed me, splinted me, and sent me home. Friend took me home. I called Dave, he agreed to take me back the next day to be casted. Doctor told me that I had a non-dislocated radial stibneal fracture.
That means two things. One, I would have healed (probably) without medical attention. It would have taken longer, hurt more, and gotten me less sympathy from professors and other people who knew me. given that I broke my right arm, the dominant arm, this would have been a bad thing.
Secondly, the radius is the lower arm bone that is closer to the thumb. I broke that bone where it gets wide at the wrist joint.
I think there is a tendency (sometimes) to want to deny pain as an indicator of serious injury. it probably happens with bleeding as well.
Another (hopefully shorter) anecdote. Dad had 2 or 3 gallbladder attacks. Mom said he should have his gallbladder out. Dad said “Someday”. Dad had an attack which turned into pancreatittis and a week in the hospital, completely out of it, on scary high doses of antibiotic and painkiller. Doctor said “You need to have the gallbladder out” Dad said “How soon can you schedule surgery”
I think the will to believe that one will heal without needing medical care can be very strong.