There are ways to communicate from the REM state back to the real world used in research on lucid dreams:
> Previously to sleeping, volunteers like Worsley agreed on preset eye movements they would perform once they achieved lucidity in their dreams, which La Berge could record in the lab.
> Previously to sleeping, volunteers like Worsley agreed on preset eye movements they would perform once they achieved lucidity in their dreams, which La Berge could record in the lab.
Source: http://dreamherbs.com/eminent-dreamers/stephen-laberge/