There is lots of evidence that the dream mode (REM) is the natural programming state of the brain - babies spend most of their time in dream state.
For babies the REM state is designed to program basic templates for living - crying, feeding, etc. In adults the REM state becomes the method we use to undo all the emotional impacts of the day. It is our system for deactiviating all the emotional triggers we have aroused, anger, fear, worry, etc.
For some people, excessive worrying or prolonged unfulfilled emotional expectations and concerns can lead to a REM state overload, and simple daydreaming (which all people slip into from time to time) becomes more vivid and real. That is, the dreaming brain seeps into the waking day.
So, any technique which helps to calm the emotions down will get to the root cause of the excessive and realistic daydreaming. Your brain has its own reality generator, and can conjure up vivid realities (as it does every night) and this generator is only activated by emotional arousal, so practice relaxation techniques to calm down the emotions.