To answer your question, dreams occur as the brain duplicates memory for long term preservation. Your dreams are a series of loosely connected concepts with no real meaning or overarcing plots. So, given that the events of the dream have no purpose and are a biproduct of biological functions, there is no requirement for them to continue where they left off, and furthermore the part where they left off can be completely unrelated to the parts that would naturally come next.
To answer your question, dreams occur as the brain duplicates memory for long term preservation. Your dreams are a series of loosely connected concepts with no real meaning or overarcing plots. So, given that the events of the dream have no purpose and are a biproduct of biological functions, there is no requirement for them to continue where they left off, and furthermore the part where they left off can be completely unrelated to the parts that would naturally come next.