Read the given passage and answer the questions that follow:
Post-traumatic stress disorder, or PTSD, is a psychiatric disorder that can result from the experience or witnessing of traumatic or life-threatening events such as a terrorist attack, violent crime and abuse, military combat, natural disasters, serious accidents or violent personal assaults. Exposure to environmental toxins (e.g. Agent orange, electromagnetic radiation) may result in immune symptoms akin to PTSD in many susceptible patients.

Subjects with PTSD often relive the experience through nightmares and flashbacks. They report difficulty in sleeping. Their behaviour becomes increasingly detached or estranged and is frequently aggravated by related disorders such as depression, substance abuse and problems of memory and cognition. The disorder soon leads to impairment of the ability to function in social or family life, which more often than not results in occupational instability, marital problems and divorces, family discord and difficulties in parenting. 

The disorder can be severe enough and last long enough to impair the person's daily life and, in the extreme, lead the patient to suicidal tendencies. PTSD is marked by clear biological changes, in addition to the psychological symptoms noted above, and is consequently complicated by a variety of other problems of physical and mental health.