Twice in my life.
I was a kid, home alone on the weekend, and I choked on some piece of food. I panicked, I tried to heimlich myself on the railing around the stairs, I went to my knees because I was weak. I thought of my parents, what a stupid way to die it was, my panic receded, I got calm. And I coughed up the food.
I hit my head on a turn/drop on a waterslide. I passed out and woke up struggling for air at the bottom of the pool. I struggled and panicked before being calm and accepting my fate. My friend saved me. The lifeguard did fuck all. My friend's dad made fun of him for dog-paddling his way down to the bottom of the pool.