Studies show that ones personality type plays a big role in the intensity of the dream experience and the amount of dream recall present in our waking life. The two types are described as thin boundary and thick boundary personalities. A Hartmann study shows that those who are classified as the thin boundary type tend to experience longer dreams, with a higher intensity of emotion, feeling, color, vividness, and interaction in them than did those classified as thick boundary types. Those who are considered to be thin boundary personalities tend to have a heightened emotional sensitivity within their dream states. The best way to describe this idea is that every type of emotion a thin boundaried person has is much more exaggerated within their dreams, which leads to the possibility of more nightmares. They do not differentiate dreams from reality like a thick boundaried person does.
What differentiates the the two boundary types is a separation between mental process, thoughts and functions. Those with thin boundary type tend to often merge thought with feeling, have a difficulty with focusing on one thing at a time, daydream or fantasize, experience forms of synaethesia, have more fluid sense of self and tend to "merge" more with those who are close to them. Those with thick boundaried personalities have much more separation between what is real and what is imaginary. They tend to have a distinct focus on one thing at a time, differentiate between thoughts and feelings, real and fantasy, self and others, lack strong memories from childhood, well organized and has a strong sense of self.
It is not to say that thick boundaried people do not suffer from nightmares, it is just that they seem to seperate the two worlds of dreams and thier waking life much more so. They also tend to do the same between their emotions and thoughts.
How does this help our understanding of Nightmares?
Reasons for the Nightmare