Compassion/Lovingkindness as soon as you wake up. Wish those people in your dreams good wishes, wish it for yourself, wish it for everyone around the world who's having a bad dream at the moment. It works. It works very well.
If you want to open it up a little more, do Compassion/Lovingkindness for any dreams that you remember as soon as you wake up. This helps us to let go of the attachments to even those nice, pleasant dreams. It helps us to wake up more refreshed, because often even the dreams that are pleasant interfere with our waking up. We're too busy thinking about that person and that thing, and it interferes. So for myself, referring to my own practice, when I wake up and I can remember any of my dreams, whether they're pleasant or unpleasant, I always do Compassion/Lovingkindness wishes for the people in the dreams, and people around the world.