There’s no hurricane or derecho — not even the hint of snow in the forecast — and yet Washington is in a weather emergency. By at least one metric, this month is the gloomiest September on record in the capital, and it is taking a subtle but substantial toll.

“Cloudy skies have prevailed on 13 of the past 16 days,” the Capital Weather Gang reported Monday, “and, no, this is not normal.”

Also not normal — the feeling of despair that has plagued many of us since August, that the sun might not come out in earnest ever again. Getting out of bed is a chore, and staying awake at work is borderline impossible, to say nothing of doing it all with a smile.

Psychologists and researchers say it’s not in your head — the weather is making you sad and lethargic at best, dejected and hopeless at worst.

“We experience the world through our sensations, and the sun is one of the crucial and central elements to energize us,” said Ani Kalayjian, a psychologist who specializes in trauma and an adjunct professor at Columbia University. “Any time the sun is compromised, we are compromised.”

Hear that, Washington? We are compromised.

The body’s circadian rhythm, its daily cycle that most obviously manifests in the form of waking and sleeping, is almost entirely controlled by lightness and darkness. Weeks of overcast skies — during which even the fleeting hint of sunshine can feel like a cruel joke — alter the chemistry in the brain and dull the circadian rhythm.

The result can be seasonal affective disorder, or SAD (appropriately), a combination of negative biological and mood-related changes that usually come on during fall and winter (gloomy seasons) and subside during spring and summer (sunny seasons). About 5 percent of Americans experience seasonal affective disorder, with symptoms lasting about 40 percent of the year, according to a 2012 article published by the American Academy of Family Physicians.

But the disorder isn’t limited to certain months or seasons, Kalayjian said. It can come on any time there’s not enough sunshine, even a particularly cloudy September.

Without bright, daily sunlight, the brain continues to produce low levels of melatonin, the sleep hormone, during waking hours. If you rise in the morning feeling as if you could spend the entire day in bed, melatonin is probably to blame. It causes fatigue and lethargy — great feelings to have when you’re trying to wind down and get a good night’s sleep; not so great when you’re presenting to the company CEO.

On gray days, the brain also produces less serotonin, a hormone that contributes to the feeling of well-being. It alters mood and emotions and notably, Kalayjian said, appetite.

“Serotonin deficiency makes you crave sugary and unhealthy carbohydrates,” Kalayjian said, which leads to overeating. If you find yourself dipping into the office candy jar more, or splurging on the pumpkin-spice latte more frequently, you might be able to blame the clouds. Kalayjian said it can turn into a vicious cycle, with guilt, self-loathing and self-punishment, which leads to worsening depression.

Most obviously, a string of cloudy days prevents us from getting enough vitamin D — something more and more research suggests is critically important and yet something we are not getting nearly enough of.

Humans evolved outdoors, where there was plenty of sunshine to be had, even on cloudy days. Now we spend the vast majority of our time inside. When the sun disappears for more than a few days in a row, what little natural vitamin D we had disappears, too.

Vitamin D is important for more than just strong bones; a deficiency is associated with cardiovascular disease, Type 2 diabetes, cancer and general increased mortality. Recent studies have linked vitamin D deficiency to obesity. It also regulates brain function and behavior, including serotonin production.

Supplementing vitamin D is one of the easiest ways to combat the gloomy feelings that come on during gloomy weather.

“Everyone should take [D3] for the entire year, especially during the dark days, because it will help balance the serotonin deficiency,” Kalayjian said. She recommends her clients take 2,000 international units per day as general maintenance, but “if you are feeling lethargic in the mornings after you had a full night’s sleep, then you definitely need 4,000 IU in the morning,” she said.

Melatonin can be taken before bed as an over-the-counter supplement and could help regulate the circadian rhythm, Kalayjian said.

Norman Rosenthal, who originally reported and named the disorder in the mid-1980s, is a strong proponent of light therapy, which has the added benefit of not requiring additional supplements and is relatively straightforward: Sit in front of a bright light each morning for 20 to 60 minutes.

Rosenthal’s original research included light therapy as a diagnosis technique, noting that people who complained of depression during the dark winter months tended to improve when exposed to more light. A follow-up described in a 2009 study showed that light therapy is effective for improving patients’ moods and that improvement was detected after the first session, with exposure as short as 20 minutes.

Whatever treatment path you decide to take to battle the September blues, know that you are not alone — there are potentially thousands of other Washingtonians who also did not want to get out of bed this morning. Plus, the sun has to come out again eventually.