mine is nowhere on the same level as most of these, but FEAR isn't about what is, it's about what you THINK is.
(false events appearing real, my dad says).

anyway, my daughter was about 2 months old. our only child. We had just moved into a new house.

around 2 am I awoke with a start to a baby's cry in the baby monitor. my blood ran cold and adrenaline spiked, because the cry sounded like a
6 month old boy, not a 2 month old girl. I envisioned strangling / choking / demon possession as I sprinted for her room.
when I got there, she was sleeping soundly. Our baby monitor must have been on the same channel as some other family in the neighborhood.

I still get chills when I think about it.

oh crap! did you die? what happened ?   tell us more.

I was never molested, just held against my will and released...I never even got a good look at him.

 

Small experimental aircraft crash.  With the sonar we used, it was easy to pinpoint exactly where they were, but you don't know what you'll find until you actually get there.  It appeared he hit the water straight-in because the craft was just shattered.  He was decapitated and the rest of his body was literally twisted around sheet metal.  Had no choice but to get up close and personal with the guy for about 30 minutes until I got him out.  Had to cut his foot off at the shin because it was stuck on some really thick metal and I didn't have time to cut the metal due to being at the very end of my allowable bottom time.  Subsequent dives, we got the craft on-deck and was able to pick out his remaining parts.

Really, really, really shitty way to die

I was so scared, my fingers refused to work.  They just curled like claws.

15 years old, deer season and 1 oz slugs whistling over my head.
My asshole puckered up so tight, I could taste shit.

Not many things have rattled me since.

A strong wind gust blew a landing helicopter's tail rotor directly above my head - within inches.  The pilot was facing the wind, and it just so happened that I was directly in line with it.  

I didn't even have the time to get really scared.  It was one of those 'oh' moments where in the next milliseconds it was dying time - there were no spare milliseconds to even have my brain make my body react.

Somehow the pilot must have been switching to elevate slightly as it happened... otherwise I would have not been here any longer.