Is there a sickness that makes you weak? Unpacking Asthenia and Chronic Conditions

September 26, 2025 •

4 min read

According to a 2021 study, approximately one-third of adults experience fatigue significant enough to interfere with their daily activities. The feeling of being drained and physically weak can be caused by various medical issues. The short answer to the question, "Is there a sickness that makes you weak?" is yes, but the specific cause can range from a temporary infection to a long-term chronic illness.

Quick Summary

Yes, many acute and chronic illnesses can cause weakness by affecting the body's energy production, immune response, or muscular and neurological function. The root cause can vary widely, from common infections and vitamin deficiencies to more complex conditions like autoimmune disorders and neurological diseases, necessitating a proper diagnosis for effective treatment.

Key Points

Causes of Asthenia: Asthenia is the medical term for abnormal physical weakness, which can be caused by a wide variety of conditions, not just a single sickness.
Acute Illnesses: Common infections like the flu, mononucleosis, and even COVID-19 can cause temporary weakness as the immune system works to fight the illness.
Chronic Conditions: Long-term issues such as autoimmune diseases (MS, RA), endocrine disorders (thyroid disease, diabetes), and cardiovascular problems can lead to ongoing, chronic weakness.
Neurological and Nutritional Factors: Weakness can stem from neurological conditions that disrupt nerve signals (MS, Myasthenia Gravis) or deficiencies in nutrients like iron or vitamin B12.
Lifestyle and Mental Health: Sedentary lifestyles, sleep disorders (sleep apnea), chronic stress, and depression can all significantly contribute to persistent feelings of weakness.
When to See a Doctor: If weakness is persistent, unexplained, or accompanied by other concerning symptoms, it is essential to consult a healthcare professional for an accurate diagnosis and treatment plan.

Understanding Asthenia: More Than Just Feeling Tired

Asthenia is the medical term for abnormal physical weakness or lack of energy. Unlike simple tiredness, which resolves with rest, asthenia is persistent and can interfere significantly with a person's ability to perform daily activities. It can be a symptom of a wide range of underlying health problems, affecting the body's systems in different ways. For some, it may manifest as localized muscle weakness, while for others, it is a generalized, full-body exhaustion.

Acute Infections

Many short-term illnesses trigger weakness as a side effect. This is a normal part of the body's immune response as it uses energy to fight off the pathogen. Examples include:

Influenza and common cold: Your immune system diverts resources to combat the virus, leading to general fatigue and muscle aches.
Mononucleosis: The Epstein-Barr virus can cause severe fatigue that can last for weeks or even months after other symptoms have disappeared.
COVID-19: Many individuals experience significant post-viral fatigue, known as "long COVID," which can persist long after the initial infection.

Chronic Medical Conditions

When weakness becomes a persistent, long-term problem, it often points to a chronic underlying condition. These diseases affect different bodily systems and can lead to ongoing energy depletion.

Autoimmune Diseases: Conditions where the immune system mistakenly attacks the body's own tissues. This includes rheumatoid arthritis, multiple sclerosis (MS), and lupus, which can cause chronic inflammation and muscle weakness.
Endocrine Disorders: Issues with the endocrine system can disrupt hormone production, which regulates metabolism. An underactive thyroid (hypothyroidism) or diabetes, if poorly managed, are common causes of profound weakness.
Cardiovascular and Pulmonary Issues: Heart disease, heart failure, and chronic obstructive pulmonary disease (COPD) can all reduce oxygen and nutrient delivery to the muscles and organs, resulting in fatigue and weakness.
Anemia and Nutritional Deficiencies: A lack of red blood cells (anemia), or low levels of essential nutrients like vitamin B12 or iron, can lead to decreased oxygen transport and general weakness.

Neurological Conditions

Disorders affecting the brain, spinal cord, and nerves can directly interfere with muscle function and strength. This can lead to more specific, localized weakness or general muscle atrophy.

Multiple Sclerosis (MS): This autoimmune disease damages the central nervous system, disrupting nerve signals and causing muscle weakness that can come and go.
Myasthenia Gravis: An autoimmune condition that causes muscle weakness by blocking nerve signals from reaching the muscles.
Parkinson's Disease: This progressive nervous system disorder affects movement and can lead to muscle weakness and tremors.

Lifestyle and Mental Health Factors

Sometimes, the cause of weakness isn't a diagnosable physical illness but rather a result of lifestyle choices or mental health issues. While these may not be a "sickness" in the traditional sense, their effects on the body are very real and should not be ignored.

Sleep Disorders: Conditions like sleep apnea can disrupt restful sleep, leading to persistent daytime fatigue and weakness.
Chronic Stress and Depression: High stress levels and mental health disorders like depression can take a significant toll on physical energy, creating a cycle of inactivity and worsening weakness.
Sedentary Lifestyle: A lack of regular physical activity can lead to muscle deconditioning and atrophy, making the body weaker over time.

Comparing Conditions Causing Weakness

To better illustrate the differences, here is a comparison table outlining several conditions that can cause weakness.


Condition	Type	Key Symptom Profile	Treatment Approach	Severity and Duration
Influenza	Acute Infection	General weakness, muscle aches, fever, cough.	Rest, hydration, sometimes antiviral medication.	Temporary; typically resolves in 1-2 weeks.
Anemia	Chronic Deficiency	Fatigue, weakness, dizziness, shortness of breath, headaches.	Iron supplements, dietary changes, addressing underlying cause.	Chronic; manageable with treatment.
Hypothyroidism	Chronic Endocrine	Weakness, fatigue, weight gain, feeling cold, dry skin.	Hormone replacement therapy.	Chronic; requires lifelong management.
Multiple Sclerosis (MS)	Autoimmune	Intermittent or progressive weakness, numbness, vision problems.	Immunosuppressants, physical therapy.	Chronic; severity varies with periods of remission.
Sleep Apnea	Sleep Disorder	Daytime weakness, fatigue, loud snoring, gasping during sleep.	CPAP therapy, lifestyle changes, surgery.	Chronic; manageable with proper treatment.

What to do if you feel chronically weak

If you are experiencing persistent or unexplained weakness, it is crucial to consult a healthcare professional for an accurate diagnosis. Here are some general steps you can take:

Keep a symptom journal: Track your symptoms, including when the weakness occurs, its severity, and any other related symptoms like pain or fatigue. This will provide valuable information for your doctor.
Review medications and lifestyle: Some medications can cause weakness as a side effect. Also, consider your diet, sleep habits, and stress levels as contributing factors.
Blood tests: A doctor may order blood work to check for common causes like anemia, thyroid issues, or vitamin deficiencies.
Specialized testing: Depending on the initial findings, your doctor may refer you for more specific tests, such as nerve conduction studies for neurological issues or a sleep study for sleep disorders.

It is important to remember that generalized weakness is a symptom, not a diagnosis in itself. It is the body's way of signaling that something is not right. Identifying and addressing the underlying cause is the most effective way to regain your strength and energy. For more authoritative information on a wide range of health topics, visit MedlinePlus.

Conclusion: Your Health is Your Strength

Persistent weakness is not something to be ignored. From minor infections to serious chronic diseases, many conditions can leave you feeling drained. The key is to listen to your body and seek professional medical advice when symptoms persist. By identifying the root cause, you can take informed steps toward a treatment plan that will help you regain your strength and overall well-being.

Frequently Asked Questions

Yes, deficiencies in certain vitamins and minerals, particularly iron (anemia) and B12, can significantly impact your body's energy production and lead to feelings of weakness and fatigue.

Yes, both anxiety and chronic stress can cause persistent fatigue and physical weakness. The body's constant state of high alert and heightened physiological response can exhaust your energy reserves.

Weakness refers to a lack of physical or muscle strength, requiring more effort for movement. Fatigue is a feeling of tiredness or exhaustion that doesn't go away with rest. The two often coexist, and one can be a symptom of the other.

While temporary weakness after a flu is normal, some individuals, especially with COVID-19 and mononucleosis, can experience post-viral fatigue that causes weakness for weeks or months after the initial infection has passed.

While common causes of muscle weakness are benign, persistent or severe weakness, especially if it is progressive or accompanied by other neurological symptoms, can be a sign of a more serious underlying condition and warrants a medical evaluation.

Doctors typically begin with a physical exam and may order blood tests to check for common issues like anemia or thyroid disorders. Depending on the patient's symptoms and health history, further testing may be required to pinpoint the exact cause.

Yes, sleep apnea causes repeated interruptions in breathing during sleep, which prevents the body from getting restful sleep. This can lead to chronic daytime fatigue and significant weakness.