I read something interesting this morning when I had my breakfast. It's about doctor office visit:

"His problem was persistent daily headaches that began the previous winter as soon as the weather turned cold. At about that time, this 37-year-old systems analyst had taken a faster-paced, better-paying job that he hoped would enable him to buy a home and replace the 20-year-old jalopy he had to drive an hour each way to and from work. After a workup that included a referral to a neurologist, CT scans and MRIs of his head and neck, and a complete laboratory survey, his doctors decided the long commute and increased job stress were causing tension headaches. But Valium and several muscle relaxants didn't help. Some well-meaning friends suggested he get psychiatric help. He remained miserable."

"When I questioned him closely, I learned that his headaches waned noticeably several hours after he arrived at work and returned soon after he got home in the evening, yet they never bothered him on weekends. Those detail gave me hunch. I asked him to  drive straight to my office after work one evening. He arrived with a splitting headache. A blood test showed an elevated level of carboxy hemoglobin, an indicator of carbon-monoxide poisoning. He got rid of that car so fast that we never found out the source of the exhaust leak that nearly cost him his life. His headaches disappeared just as fast."