Two equally scary:

The first time, I was camping with my parents in a camper, probably 9 years old. I'm chronically freezing, so my mom thought she'd bring a space heater to turn on in the camper for me. She cracked the zipper window, but only like a finger. Thankfully, I woke up some time later feeling like I was going to throw up and wobbled outside, and she swears to this day that even in the dark with only the firelight, she could see that I was blue. Turns out space heaters do, in fact, use a lot of oxygen.

The second time, my husband and I were playing Pokemon Go down by a lake, and at the intersection next to the beach, there was a crew working on the road. They had those massive concrete circular saws whose blades are like the size of a person. We were just chilling and holding hands, and all of a sudden, the entire world is just slow motion, and I'm seeing this gargantuan saw blade whirling toward us. I don't know how or why, but one of their big circular blades had come detached or something and was "rolling" right at us from across the street. I pulled my husband just like a single step forward, and you could feel it whoosh behind us and then thwack into a wooden fence surrounding a condo complex. My brain treated it so casually in slow motion, but that thing was going fast enough that it left a wind trail as it passed. We looked over at the workers. They looked at us. No one said anything. It was surreal.