Jet lag, also known as desynchronosis or flight fatigue, is defined as “extreme tiredness and other physical effects felt by a person after a long flight across several time zones.” Besides insomnia, symptoms of jet lag include weakness, fatigue, dehydration, body aches, diarrhea, dizziness, headache, irritability, and memory loss. Jet lag is one of the circadian rhythm disorders; others include shift work disorder, sleep phase disorder, and irregular sleep-wake rhythm.

Symptoms of jet lag usually occur within a couple of days of travel. The more time zones crossed, the longer and more severe the symptoms; a good rule of thumb is that recovery takes a day for every time zone crossed. Easterly travel has been linked to a worsening condition. Because north-south travel doesn’t cross time zones, jet lag is supposedly not a problem — even after long flights.

Jet lag is believed to be a result of a disturbance in the circadian rhythm, originating in the brain. The body’s innate clock is located at the base of the hypothalamus, where a bundled pair of nerve cells known as the suprachiasmatic nuclei coordinates the sleep-wake cycle through hormones, core temperature, and electrical impulses via the autonomic nervous system.

Jet lag is not a life-threatening condition. Treatment is aimed at mitigating its symptoms. Since the light-dark cycle is critical to the proper maintenance of our circadian rhythm, exposure to natural or artificial light can assist in readjusting the body’s clock. Other strategies include the timing of meals and naps, staying hydrated, exercising, and the judicious use of melatonin and other over-the-counter or prescription medications.

Most emergency physicians have experienced the symptoms of jet lag: even those who have never traveled a day in their lives. As shift workers, we are prone to the fatigue, weakness, and sleep disturbances that occur whenever we flip from a diurnal to a nocturnal work schedule. But the generalized malaise we endure while attempting to readjust our body’s clock tends to be different in quality from that experienced after a long flight through various time zones. I became acutely aware of that observation only recently.

During the past fifteen months, I have been traveling back and forth between the southwest and the northeast. I’m an emergency physician and a writer. I split my month between Las Vegas and New York City; I work a string of day and night shifts in Las Vegas, then I fly across the country and spend the remainder of the month working on my next novel at various coffee shops around Brooklyn.

When I first started my interstate travel a year ago, I noticed something peculiar. The day after arriving to New York, I started feeling the same symptoms I did after every other flight, or after working a string of overnight shifts, but I noticed that the generalized malaise, the fatigue, and the weakness were different (i.e. the quality of the symptoms were different). I also noted mild rhinorrhea, some sneezing, and a slight headache. I felt dehydrated and suffered from myositis and body aches, even though I made sure I stayed hydrated and active during the flight. These symptoms occurred whether I flew east-west or north-south.

This prompted an idea, which has been brewing in my mind for the past few months.

What if the jet lag symptoms experienced by some travelers are due to a mild subacute viral syndrome?

Let’s consider this possibility for a moment. Travelers of commercial airlines are confined to a metal tube with hundreds of people for multiple hours. There is very little one can do to prevent being exposed to a plethora of potentially infectious pathogens.

Putting personal experience aside, each day dozens of Las Vegas tourists present to the emergency department with a nonspecific, viral-like illness twenty-four to forty-eight hours after arriving to the city by commercial flight. Although it may be pure coincidence (after all, nearly forty-million visitors come to Las Vegas every year), one has to consider the possibility of a common infectious etiology. Lack of sleep and an alteration of the circadian rhythm can also account for the high numbers of patients presenting with viral symptoms since either can impair one’s immune system and make an individual susceptible to infection.

Regardless of etiology, there is no need to panic. Most commercial airlines ensure that the air inside their cabins is circulated quickly, sifted and scrubbed through HEPA filters, “which can catch 99.9% of pathogens, including viruses.” I’ve traveled dozens of times and I haven’t had anything worse than the sniffles. The purpose of this essay is to raise the possibility that the entity known as jet lag may not be just a result of a circadian rhythm disturbance. It could also be part infectious, either a result of being exposed to pathogens from fellow travelers or due to a weakened immune system from lack of sleep.

Either way, physicians should consider the potential health risks of air travel and not pigeon hole themselves to a diagnosis of jet lag whenever a tourist presents to the emergency department with a complaint of generalized malaise or other nonspecific symptoms. With nearly two billion people traveling aboard commercial airlines each year, we should always consider the other causes of potential life-threatening illnesses associated with flight, including deep venous thrombosis and exacerbations of chronic medical conditions. If a patient does present to the emergency department with a simple case of jetlag-itis, you can instruct them to rest, to drink plenty of fluids, and, in Las Vegas, to refrain from gambling or engaging in other high-risk activities.

Alberto Hazan is an emergency physician and author of Dr. Vigilante and The League of Freaks series.