1.   Interviewers asked about smoking habits and used special surveys designed to identify psychiatric problems, including anxiety disorders.

2.   Less common causes include genetic disorders, chemotherapy for cancer and viral and other infections.

3.   The condition may also be associated with ailments, including thyroid disorders, and may flare up after injury, stress or severe sunburn.

4.   The military, anxious for conscripts, often drafts people with serious health problems, including mental disorders.