10 Hidden Causes of Fatigue You Might Be Overlooking

We all know about anemia or thyroid disorders as common causes of fatigue. But what if your doctor tells you your labs are “normal” and you’re still exhausted?

That’s the frustrating truth for many women I see in my practice: their tiredness is real, but the answers aren’t obvious.

Fatigue is rarely caused by just one thing. Instead, it’s often the result of hidden stressors in the body that quietly drain energy over time. In functional medicine, we go beyond the basics and investigate these root causes.

Here are 10 often-overlooked reasons you might be feeling so drained—and what to do about them.

1. Medications You’re Taking

We don’t often think about side effects unless they’re dramatic, but many common medications list fatigue as one of the top complaints.

• Examples: blood pressure medications (beta blockers), antihistamines, birth control pills, statins, and even some antidepressants.

• Why it matters: Medications can alter how your body metabolizes nutrients, regulate hormones, or even slow down your heart rate—leaving you less energized.

💡 If you notice fatigue started after beginning a new medication, talk to your doctor about alternatives or supportive strategies.

2. Gut Imbalances

Your gut is often called your “second brain”—and for good reason. The trillions of microbes living there influence digestion, nutrient absorption, inflammation, and even mood.

• Hidden cause: Dysbiosis (too many “bad” bacteria compared to good), yeast overgrowth, or poor digestion can keep your body from extracting fuel from food.

• Symptoms to watch: bloating, constipation, diarrhea, brain fog, or sugar cravings.

When your gut is off balance, your body may be starved of key vitamins and constantly fighting inflammation—leaving you chronically tired.

3. Stealth Infections

Not all infections announce themselves loudly with fever or chills. Some “smolder” quietly in the background.

• Examples: Epstein-Barr virus reactivation, Lyme disease, chronic sinus infections, or hidden urinary tract infections.

• Why it matters: These infections keep your immune system in a low-grade fight, burning energy reserves around the clock.

Many of my patients describe it as “I wake up tired no matter how much I sleep.” That’s your immune system doing overtime.

4. Stress Dysregulation (“Burnout”)

You’ve probably heard of “adrenal fatigue”—but what’s really happening is a breakdown in your body’s stress regulation system.

When stress hormones like cortisol stay high for too long, your body eventually loses the ability to keep up. The result? You swing between wired (can’t sleep, racing mind) and tired (total crash).

This pattern is common in women juggling family, work, and caregiving—where stress feels unrelenting. Left unchecked, stress dysregulation can mimic thyroid disease, depression, or chronic fatigue syndrome.

5. Nutrient Deficiencies

Even with a healthy diet, it’s surprisingly easy to run low on essential nutrients:

• B12: needed for red blood cell and nerve function.

• Iron: crucial for oxygen transport.

• Magnesium: involved in over 300 energy reactions.

• Vitamin D: essential for mood, immunity, and energy.

Modern farming practices, stress, medications, and gut issues all interfere with nutrient absorption. That’s why labs for nutrient status often reveal missing pieces in the fatigue puzzle.

6. Hormone Shifts

Hormones are your body’s messengers—and when they fluctuate, energy often follows.

• Estrogen & Progesterone: Women often notice fatigue worsen in perimenopause, postpartum, or after coming off birth control.

• Testosterone: Low levels in both men and women can sap stamina and motivation.

• Cortisol: The stress hormone, when out of rhythm, can cause morning grogginess or 3 pm crashes.

When hormones are overlooked, fatigue becomes a moving target that’s hard to pin down.

7. Blood Sugar Swings

Do you feel energized after eating… only to crash an hour later? That’s blood sugar at work.

• Spikes from refined carbs or sugary snacks trigger insulin surges.

• The quick drop that follows leaves you tired, shaky, and craving more sugar or caffeine.

Over time, these swings contribute to insulin resistance, inflammation, and yes—persistent fatigue.

Stabilizing blood sugar through balanced meals (protein, fiber, healthy fats) can transform daily energy.

8. Sleep Quality (Not Just Quantity)

You might be in bed for eight hours, but the real question is: are you moving through all the restorative stages of sleep?

• Obstructive sleep apnea: causes micro-awakenings you may not notice.

• Restless legs syndrome: disrupts deep sleep.

• Nighttime cortisol spikes: wake you at 2–3 am with racing thoughts.

Quality sleep restores your brain, hormones, and energy systems. Without it, you’re running on half a battery every day.

9. Chronic Inflammation

Think of inflammation as a fire inside the body. If it’s smoldering—whether from food sensitivities, autoimmune activity, or unresolved injuries—it’s constantly consuming resources.

Your body diverts energy to “fight” rather than fueling your daily life. Common hidden culprits include gluten sensitivity, undiagnosed autoimmune conditions, or even gum disease.

10. Environmental Exposures

We live surrounded by chemicals, pollutants, and toxins our grandparents never faced.

• Mold exposure: can trigger brain fog, fatigue, and allergies.

• Heavy metals (like mercury or lead): impair mitochondria, the energy factories in your cells.

• Household chemicals: may burden your detox pathways.

While you can’t live in a bubble, identifying and reducing exposures can have a profound impact on energy.

Why This Matters

Fatigue isn’t a character flaw—it’s a symptom. Your body is whispering (or shouting) that something is out of balance.

Instead of masking it with caffeine, sugar, or sheer willpower, the functional medicine approach is to ask why. Why is your body struggling to make or use energy? What’s the root cause?

✨ Next Step: If you’ve been told “everything looks fine” but you still feel exhausted, it’s time to dig deeper. Schedule a Discovery Call with me, Dr. Joan, to uncover what’s really draining your energy and take your first step toward lasting vitality.