A moment were you had the false impression you were close to death.

For me:

-Panick attack. I had a stressful internship, and one day, it materialized with a panick attack. Suddenly, i was increasingly paralysed, my skin became insensitive, had heavy tinglings, had hard to breath. I though "that's it, i'm about to die" and managed to call the ambulance. Of course, by the time it arrives, the crisis had stopped, but i went to hospital anyway. This is were i learned that it was a panick attack, and that was not a vital emergency. If you don't know what it is, you're really convinced you're dying.

-When i tried a blood donation. My blood pressure lowered rapidly, i became weaker and weaker and feeling increasingly bad, they had to stop the process.