Childhood
Freud suggests that dreams often take on certain flavors in regard to their concrete and abstract imagery. He says that a person should not be surprised to be in feelings and situations (or even beliefs) that are properly childish. There is a sense in which memories from childhood still matter in daily life, so perhaps this is one reason a dream might reduce a person to their childhood emotions, but then again, there is a deep mystery here, because a person might encounter those moments and feel that they are deeply true.
Death
Death imagery is also a central aspect of what a dreamer might expect from their dreams. Concrete symbols suggesting death are often, like a train on its final departure, or the encounter with a dead loved one, or the haunting by a ghost or entity, or a religious epiphany about the afterlife—the spectrum here is quite large. The question of death is one that the human body is particularly interested in exploring, because many human instincts have to do with avoiding death, so a dream might "center" a person's psyche around that essential dilemma again through symbols and emotional dynamics.
Sexuality
A person's sense of sexuality is fair game in a dream. This imagery runs the gamut from wet dreams in adolescence, through dreams of sexual betrayal, and then beyond into more sublime territory. Freud is famous for seeing sexual imagery where others would not necessarily see it. He sometimes feels that a concept or symbol is inherently sexual, even when it seems benign, as when a person dreams about their fondness for a parent—especially there, he senses sexual imagery, even the pseudo-sexual imagery of latent sexuality (like a child's latent sexuality).
The sublime
Finally, Freud observes that a dream can take on strangely exotic, surreal, and hellish imageries. These can be categorized under the broad umbrella of the "sublime." Religious ecstasy can be called sublime, or a nightmare can be sublime (so the term is truly broad). The sense of the imagery is just that there is far more implied than originally suspected. For instance, a person who climbs a mountain in their dream might realize that a mountaintop experience has implications that extend past the limits of their own consciousness or life. This is sublime imagery, because it implies something supernatural. A dream can be composed of these supernatural questions.
