When were you most scared?

For the whole of the Easter Weekend I have been either sleeping or working, and the night shifts have been busy ones.
The Prof has been pleasantly sanguine about the ruination of his one of all-too-few holidays, a fact that I put down to chocolate and some downtime with the children.
Mrs Trellis dropped off a couple of Easter bunnies too, which was nice of her, she asked if the Flower Show had indeed been cancelled this year as per village gossip.
I assured her that it had not, and promptly conscripted her in the boiled fruit cake class.

Over the weekend one of my patients likened his admission to intensive care to one of the "most frightening experiences of his life". The " most" as it turned out, was a time when he was attacked by a lioness in Africa, a story that unfortunately we were unable to catch up with throughout the shift.

But it got me thinking.....what WAS the most frightening experience I have ever suffered? 
HUMMMMM.....

Well, my answer must, thankfully,  be very few indeed, !
Anything to do with heights really freak me out,so the time I found myself alone on the observation deck of the Seattle's Space needle in a rainstorm would figure high on this list.
The time I was attacked by a Russian terrier ( the leader and most aggressive member of a pack of nine housedogs) still brings shivers to my soul when I think about it, as does the time I was first attacked my a psychiatric patient whilst on duty.
But these are just minor scare times compared with a man facing down a lioness in the African bush!

So tell me!
What was your most frightening experience EVER.
I'd be interested to know.