Why do we get a falling sensation as we drift off to sleep?

This week, Dr Chris Smith and Sara Jayne Makwala King get to the bottom of IBS, why women living together often synchronise menstrual cycles, why we get a sudden falling sensation when dropping off to sleep sometimes, and if Earth suddenly stopped spinning, what would happen first? Also, are the faces that crop up in our dreams real people we've seen before, or has our brain created people that don't actually exist? Like this podcast? Please help us by supporting the Naked Scientists (thenakedscientists.com/donate)