What is a Dream?
To understand Christian dream symbols and better understand the dream itself, we first need to start at the beginning - what is a dream?
Dreams can be defined as a single image, series of sequential images, entire scenarios (i.e., a play) occurring involuntarily during sleep. But dreams are actually one of the least understood human phenomena despite all of the recent research on the topic of dreams. We know the brain and body need to rest and thus sleep occurs, but our brains are still very active, particularly during REM (Rapid Eye Movement) sleep. We typically have what we would call dreams anywhere from three to six times per night, although hardly any of us recall even a single dream consistently every night. But we know this occurs through observing brain waves and eye movements during REM sleep patterns. REM sleep only accounts for about 25% of a total night's sleep but this is where we have the most vivid dreams, and these occur most frequently a few hours before dawn.
So we likely experience Christian dream symbols and recall those most vividly as these occur during REM sleep cycles. See also Dreams vs. Visions and Lucid Dreaming discussing different kinds of experiences besides picturing Christian symbols in a traditional dream.