Constantly Exhausted? 5 Hidden Causes of Fatigue Your Doctor Wants You to Know

Do you feel like you are running on empty no matter how much sleep you get? At Hopkins MD, our lead physician Dr. Tom Hopkins, M.D. and our team of eight dedicated providers help patients in Roseville, California and Lincoln, California uncover the root biological reasons for their low energy. We know that chronic exhaustion is rarely just a lifestyle issue. In fact, a recent report by the Centers for Disease Control and Prevention (CDC, 2024) revealed that 16.6% of American adults experience frequent, severe fatigue most or every day. If you are constantly exhausted, here are five hidden causes of fatigue we look for during a comprehensive Primary Care evaluation. 

What are the 5 hidden causes of fatigue?

To truly address persistent exhaustion, we must look beyond basic blood tests. Here are five scientifically proven, underlying reasons why your energy levels might be bottoming out:

1. Iron Deficiency Without Anemia (IDWA)

Many people believe you only lack iron if you are anemic, but this is a common misconception. Your mitochondria—the energy powerhouses of your cells—rely on iron to produce cellular energy. A study in the Journal of Cachexia, Sarcopenia and Muscle (2022) found that depleting your iron stores (measured by ferritin) causes severe physical exhaustion and brain fog, even when your red blood cell counts look completely normal.

2. Atypical Sleep Apnea in Women

Obstructive sleep apnea (OSA) is not just a "snoring man's disease." In women, sleep apnea often presents as insomnia, morning headaches, and daytime fatigue rather than loud snoring. According to research in Sleep Medicine Reviews (2025), this atypical presentation leads to a massive 75% underdiagnosis rate in women, leaving them chronically sleep-deprived.

3. Mitochondrial Dysfunction and Long COVID

If you have never felt the same after a viral illness, your cells might be struggling to produce energy. Clinical studies show that Long COVID fatigue affects up to 65% of patients. The virus can damage autonomic control centers in the brain and disrupt mitochondrial function, leaving tissues starved of oxygen and energy.

4. HPA Axis Dysregulation (Burnout)

While "adrenal fatigue" is a popular myth, chronic stress does cause real, measurable biological changes. Ongoing occupational or personal stress dysregulates the Hypothalamic-Pituitary-Adrenal (HPA) axis—the brain-to-body communication system. This dysregulation flattens your daily cortisol rhythm and triggers systemic inflammation, causing profound somatic fatigue.

5. Unaddressed Age-Related Factors

When older adults feel exhausted, a slightly elevated thyroid-stimulating hormone (TSH) level is often blamed. However, clinical trials show that treating mild subclinical hypothyroidism with synthetic hormones rarely improves fatigue in seniors. Instead, age-related exhaustion is usually driven by other factors like muscle loss, medication side effects, or nutritional gaps.

How we help you reclaim your energy

At Hopkins MD, we do not believe in one-size-fits-all solutions for chronic exhaustion. We combine traditional primary care with integrative wellness strategies to build a personalized treatment plan for you. Whether you need targeted Nutritional Supplements to correct a hidden iron deficiency, or specialized Behavioral Health and Wellness support to manage chronic stress and HPA axis dysregulation, we are here to guide you. We focus on finding the true root cause of your symptoms so you can feel vibrant again.

You do not have to live with constant exhaustion. If you are ready to uncover what is draining your energy, contact our team today to schedule a comprehensive wellness consultation at our Roseville or Lincoln offices.