It represents lot of things; few of what I feel is;
Dreams represent the status of mind. Whatever is affecting sub-cautious mind in the day will reflect nearby in the dreams with different forms.
Dreams are affected by intuitions, Some times its shows what will happen in future. Other logic's are also applicable here.
Dream can be affected by in-appropriate way of sleep. If someone has the weight over the chest after sleep begins, then scaring dreams is 100 % possible because of the weight on hearts affecting the nervous system.
Another reason of dream is almost the same like above, the in-appropriate way of sleeping. If someone feels heavy urination after sleeping, then it will leads to frequent dreams.
Other then this many other reasons affects dreams. I will be glad if you find this useful.