It was left deliberately vague whether Q really caused that experience. Though I find either way very plausible. I prefer the explanation that it was Q behind the whole ordeal because it's the more interesting explanation. Though it is likely he would have survived by Crusher's expertise had Q not intervened.
For me there's no specific moment that changed the course of my life, but I'd certainly like to change the person I was back in high school and college. I was set back years in more ways than one because of how I behaved in certain parts of my life.