A fighter pilot had unexplained headaches for over a year. The cause was hiding in plain sight.

The patient: A 29-year-old man in India The symptoms: The man, a fighter pilot in the Indian Air Force, went to a civilian neurologist after having persistent headaches for 18 months.

The headaches would occur approximately two to three times per month, starting in the late afternoon and lasting up to three days.

Sleep did not improve his symptoms.

The pain was typically greater on the right side of his head, but he would often feel pain on the left side as well.

The pilot also reported that just before a headache, he would experience a "sense of lousiness," his doctors wrote in a report of the case .

Sometimes, the pain was so intense that the man was unable to take part in scheduled flights.

If he flew anyway during an episode, his headache would be even worse the next day.

What happened next: According to the man, his finances and personal relationships were not a source of stress. (Stress, in general, is a very common headache trigger .) When asked about his medical history, the pilot recalled no recent ailments or conditions that could cause recurring headaches, such as inflammation and congestion of the sinuses (sinusitis).

He had no family history of chronic headaches or migraine, a neurological disease that frequently causes moderate to severe headache, among other symptoms .

Nor did he experience nausea, vomiting or visual anomalies called "auras," which often accompany or precede migraines.

Nevertheless, the civilian doctor determined that migraines were the culprit.

He prescribed divalproex ‪—‬ an oral medication used for migraine prevention — and told the patient that he would likely need this medication for years.

Concerned about taking the drug over a long period, the pilot decided to consult an authorized specialist at a military medical facility for further evaluation.

The diagnosis: The military doctors reviewed the pilot's case and examined him.