When we sleep we go through different stages. When we first fall asleep we are in stage 1 which is a light sleep and progressively we move into deeper and deeper sleep (stage 4). We then cycle down until we approach stage 1 in which we enter a different kind of sleep Rapid Eye Movement (REM). It is in this stage in which we begin to dream. We then go back and forth in between REM and NREM (when we don't dream).
Something interesting happens when we are in REM, our bodies become immobilized which is a protection from acting out our dreams. Also a study was conducted by Dement that showed that we need to dream and in fact if a person goes without dreaming the next night they will end up dreaming more than usual. Also in the study it showed that there was a slight increase of weight gain by not being allowed to dream.
As we write sleep into our characters lives we need to understand their sleep patterns and how they work. Are they getting deprivation of sleep and/or dreams? They should be having the "big" dreams in the morning when more people have dreams or is this what makes the dream unique because it happens immediately upon falling asleep.?. Dreams can be a great way to move our characters and to give insight into our story to our readers. It is also a great way to show foreshadowing.
How do the dreams affect our characters? Do they believe in the dreams they are having? Are they grouchy for the rest of the day? You know the days I'm talking about you wake up after dreaming about fighting with significant other and you are angry at them for the rest of the day.
Keep in mind the sleep patterns of your characters and how all that sleeping on hard ground is affecting them. How do you interpret your dreams?