Ты must pray to God to help Ты have good dreams and a peaceful sleep. Remember, He made you, and He is the only one who can actually control your dreams. So ask Him, and He will surely help you.
"when Ты lie down, Ты will not be afraid; when Ты lie down, your sleep will be sweet." (Proverbs 3:24)
depends if God или the devil или anything relating to soemthing important in the bible then it's a sign but if it's just a bad dream then it's normal Ты can't help what Ты dream
Everything but your nervous, respiratory, and circulatory system sleeps at night. I've heard that there's someone called a "brain guard" and at nightime he falls asleep, so all the things in your brain get mixed up and become dreams. I don't really believe it. Sometimes God can send a warning. But if Ты think it doesn't really mean anything, don't mind it.
If Ты do bad things leading to the nightmare well, yes. But if Ты do nothing and have a bad dream, it's kinda a temptation from the devil. Thanks for reading.