Which of the following is a characteristic of distress?

Difficulty sleeping or nightmares are indeed characteristic of distress. When a person is experiencing distress, they often face overwhelming emotions, anxiety, or negative thoughts that can affect their ability to relax and sleep properly. This state of mental strain can lead to insomnia or disrupted sleep patterns, which may manifest as difficulty falling asleep, staying asleep, or experiencing nightmares.

The other characteristics listed, such as increased levels of ambition, prolonged relaxation, and enhanced focus and concentration, are not typically associated with distress. Ambition and enhanced focus may be signs of a positive drive or motivation, while prolonged relaxation is often indicative of a state of well-being or contentment, both of which are contrary to the feelings experienced during periods of distress. Thus, the presence of difficulty sleeping or nightmares serves as a clear indicator of an individual's struggle with distress.