There are physical, psychological, and physiological reasons for dreaming.
Physical factors are people sleep, may be nerve cells are widely inhibited, but this inhibition process is incomplete, the cerebral cortex of some of the nerves are still in a state of excitement, and thus produce a dream, such as flying birds over the top of the head will dream of taking off belongs to the physical stimulation caused by.
Psychological factors, if the daytime overthinking, or suffered great sadness and joy, thinking about the west, the night will also dream. If you miss someone in particular, you will see that person in your dream.
In terms of physiological factors, the sensations of the internal organs of the body during sleep will affect the occurrence of dreams. For example, people who are hungry dream about food, and people who are anxious to urinate dream about looking for a toilet.
If you experience symptoms of excessive dreams and disturbed sleep, it is recommended that you visit a hospital promptly for early and regular treatment.