Brain aneurysm is truly something terrible, I lost a friend to it a couple of years ago. (She was 22 at the time and in good health). She just woke up one day in the middle of the night with a headache and had to vomit. On the way to the hospital she fell into a coma and never woke up. Really scary.
My significant other (23 at the time, otherwise perfectly healthy) felt a sudden headache one evening. Since it didn't stop, she was taken to the emergency room immediately, where they've dismissed her with "menstrual problems". A day after that the pain didn't stop, she ended up in the hospital, and had a (fortunately successful) brain operation some days later. Luckily it was in an accessible place, so she ended up…
Infuriating.