Why do we have bad dreams? The Huffington Post published an article that gave six reasons. They were stress and anxiety, spicy foods, fat content of food, alcohol, drugs and illness. http://www.huffingtonpost.com/2008/12/30/six-reasons-we-have-bad-d_n_154183.html
But what does G-d say about the matter?
The purpose of a bad dream, which predicts dire events, is to give us the opportunity to actually alter the negative decree. By changing our behavior and aligning ourselves with the will of our creator, we are able to change the future. If a person did not have a chance to preempt the evil occurrence through proper behavior, G-d would not have sent the dream in the first place.
In addition, there are four types of dreams that come true: an early morning dream, a dream about someone else, a dream whose meaning is interpreted within the dream itself, and a dream that is repeated.
So the next time you have a bad dream, think of it as an opportunity to change your future in a positive, healthy way.