What is a common symptom of Post-Traumatic Stress Disorder (PTSD)?

Flashbacks or intrusive memories are hallmark symptoms of Post-Traumatic Stress Disorder (PTSD). Individuals with PTSD often relive the traumatic event through vivid recollections, nightmares, or dissociative episodes where they feel as though they are experiencing the trauma again. This symptom is directly related to the distress and anxiety that can arise from the traumatic experience, leading to significant disruption in the individual's daily life.

In terms of the other choices, oversleeping may occur in some individuals with PTSD due to avoidance or depressive symptoms but is not as specifically tied to the disorder. Compulsive checking behaviors can be associated with anxiety disorders, including Obsessive-Compulsive Disorder, rather than PTSD. Mood swings can also occur in a variety of mental health conditions, but flashbacks are distinctly identified as a core symptom of PTSD. Thus, the specificity of flashbacks or intrusive memories to PTSD distinguishes this choice as the correct one.