It Might Be Medical
Your energy shouldn't stay low for longer than two weeks; if it does, it's likely a symptom of something serious. We asked Jeffrey J. Cain, M.D., president of the American Academy of Family Physicians, and Amy Bader, N.D., of the National College of Naturopathic Medicine, what to have your doc test for.

Condition: Anemia
Indicator: Too few red blood cells
Culprit: A diet lacking in iron or vitamin B
Countermeasure: "Talk to your doctor about medication for gastrointestinal issues," Bader says.

Condition: Type 2 Diabetes
Indicator: High blood-sugar levels
Culprit: Too much fat on your frame—even if you're a normal weight (a.k.a. being "skinny fat")
Countermeasure: Exercise more and start eating healthier. No help? "You may need an Rx for insulin," Cain says.

Condition: Adrenal Fatigue
Indicator: An overage of cortisol from a hyperactive adrenal gland
Culprit: Mental or physical stress (from work, food sensitivities, etc.)
Countermeasure: "Cut out sugar to reduce inflammation," Bader says. Also, relax with yoga or meditation.

Condition: Low T
Indicator: Diminished production of testosterone
Culprit: Stress, inflammation, and exposure to estrogen
Countermeasure: Drop excess weight and avoid alcohol, especially beer. "Hops are major estrogen promoters," Bader says.

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(Almost) Instant Rocket-Fuel
Sure, caffeine is classified by the FDA as a drug, yet it's still the go-to stimulant when you're dragging (because it blocks the reception of the sedation-inducing hormone adenosine). Multiple studies have shown it can even improve reaction times and athletic performance. But if your Red Bull or Diet Coke addiction is getting out of hand, consider natural supplements as an alternative. "They offer a milder, longer-term boost," says Amy Bader, N.D., an adjunct clinical faculty member at the National College of Naturopathic Medicine in Portland, Oregon. Her two favorites (both available in supplement form at health-food stores, though you should take only one or the other) should have you experiencing more all-day drive after about two weeks.

Maca is a root that was used by Peruvian warriors to increase stamina, libido, and vigor. It also appears to stimulate the endocrine system and balance hormones.

Rhodiola rosea, a.k.a. Arctic root, is a Siberian herb that can help with muscle recovery, stamina, mental clarity, and concentration. It also may help boost neurotransmitters—brain chemicals such as serotonin—which help us feel happier and more energized.

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+ Stop Blaming SAD
Don't confuse sluggishness experienced in the cold-weather months with true seasonal affective disorder (SAD). David Kerr, Ph.D., assistant professor of psychology at Oregon State University, says, "Most of us don't like the dark, cold, wet winter. We don't have as many pleasant memories associated with it and we're less active. But having less fun is not the same as having clinical depression."

If your feelings of listlessness last for more than two weeks, happen annually, and are getting in the way of your social life, ask a doctor about light therapy—which uses a special light frequency to treat all forms of depression, including SAD. (PSA: Don't try this on your own. Talk to an M.D. to determine the correct time of day and duration.) Otherwise, reframe your outlook. "Treat those dark days like anything else you dread—dentist appointments, a work event—and find ways to make the most of them," Kerr says.