Overall I liked the story.
But I felt I was promised a story about a rash of children who were mysteriously strangling themselves to death, and that this was somehow sexual in nature. I found this very original and disturbing. But then I was delivered a story about no-the-aliens-are-real, which is pretty well worn ground.
Pet peeve: Instead of saying, "you know I think it might be sexual," people who say "obviously it's sexual, and if you are skeptical then you are a Victorian prude." I think this is a minor quibble, but Bear does spend some of the most valuable real estate in the story making this point.
And to satisfy the informal poll: I did the thing where you hyperventilate, stand up quickly, then faint. It was going around a summer camp when I was about 10. Got a cool buzz, weird images that were dreams but not dreams, but nothing sexual.