This is why I don't even think about trying lucid dreaming ._.
Lucid dreaming is safe and is not harmful. He experienced what is called sleep paralysis. It is temporary. The throwing up is not directly related and is
very unusual. I've been involved in lucid dreaming for many years and I've never heard of such a thing happening. My initial thoughts are he panicked, which is unnecessary.
If you are enduring anything, you are doing it wrong.
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Were you aware you were asleep? Lucid dreaming is only about being aware you are in a dream. It is not about having strange dreams, vivid ones, or even being able to control them. Its black and white; you realize you are dreaming or you don't.
Just advice to anyone here: even if you don't try to lucid dream, you will and have experienced sleep paralysis whether you realize it or not. All of these so called "horror stories" aren't related to lucid dreaming, they are related to falling asleep in general. They are just noticed because the personal is actively aware of the sleep process.