I wouldn't make much out of it. He/she probably just had a nightmare, whether it was lucid or not its hard to know. Even if it was, this doesn't mean its gonna happen again, or that LDing causes this to an individual. Don't worry about this, I would really not make much of this, cause if you do, your subconscious could play a trick on you and make your next LD a nightmare...

If that happens, don't worry, just know that you can wake up whenever you want, or, if you have the posibility to do so, you can just confront it...