Myalgic encephalomyelitis/chronic fatigue syndrome

Some people feel a very deep tiredness.

This feeling does not go away with rest. Doing small things can make them feel worse. This can happen a day or two later. It might last for many months.

They may also feel dizzy when standing up. It can be hard to think clearly. This can happen to kids or adults. Many people with this illness are women.

It is a hard thing to live with.

Some people live with a long-term illness called ME/CFS.

This illness causes very deep tiredness. Rest does not make it go away. This tiredness can feel like having the flu. People may also feel dizzy when they stand up. This is called orthostatic intolerance. It means the body has trouble staying steady while upright.

One main part of ME/CFS is called post-exertional malaise, or PEM. PEM is when symptoms get much worse after activity. This activity might be physical or even mental. It can happen right away or a few days later.

These "crashes" can last for many months.

Other symptoms include pain and "brain fog." Brain fog makes it hard to think or remember things. Many people also have trouble sleeping well. They may wake up feeling very tired. ME/CFS can happen to people of all ages. It is more common in women and middle-aged people.

Doctors do not know the exact cause yet. Many cases start after an infection.

Myalgic encephalomyelitis/chronic fatigue syndrome, or ME/CFS, is a disabling long-term illness.

It causes a very deep fatigue that rest cannot fix. People with this condition often struggle with sleep and memory. Some people also feel dizzy or faint when they stand up. This feeling is called orthostatic intolerance. It can happen because the body has trouble staying steady while upright. This illness can be very hard on a person's social life.

About one quarter of those affected cannot leave their homes or beds.

The most important symptom is called post-exertional malaise, or PEM. PEM is a worsening of symptoms after doing an activity. This activity could be physical, like shopping, or even mental. It might even be something small like taking a shower.

PEM often starts 12 to 48 hours after the activity. It can also happen immediately. These "crashes" can last for hours, days, or even many months. This makes it very hard to plan a normal day.

Doctors are still learning about the history of this illness. The World Health Organization has called it a neurological disease since 1969. This means it affects the nervous system. Some people also call it a neuroimmune condition. This is because it involves the immune system too. Many names have been used for this illness over the years. Some people use the name chronic fatigue syndrome. Others prefer the full name, ME/CFS. In 2015, a report suggested the name systemic exertion intolerance disease.

There are many important facts to know about who gets ME/CFS. It affects two to nine out of every 1,000 people. The illness is more common in women than in men. It often happens to people in middle age. However, it can happen to anyone, including children.

Between 60% and 80% of cases start after an infection. One common trigger is infectious mononucleosis. Many people also fit the criteria after having long COVID. There is currently no laboratory test to diagnose it.

Understanding ME/CFS helps us see how it links to other things. It is similar to other conditions that follow an infection. For example, long COVID and Lyme disease share many symptoms.

People with ME/CFS often deal with "brain fog." This makes it hard to find words or concentrate. It can feel like the brain is processing information very slowly. Managing the illness often involves a method called pacing. Pacing means balancing activities to avoid a crash. This helps people manage their limited energy levels.

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a complex and disabling chronic illness. It is characterized by profound, persistent fatigue that is not relieved by rest. This fatigue is much more severe and long-lasting than normal tiredness. It can significantly reduce a person's ability to function in daily life. The illness affects many different body systems, including the nervous and immune systems. It also appears to involve changes in how the body produces energy.

The hallmark symptom of ME/CFS is post-exertional malaise, often called PEM. PEM is a worsening of symptoms following physical, mental, social, or emotional activity. This activity can be very minor, such as taking a shower or shopping for food. Even being in a stimulating environment can trigger a response. PEM typically begins 12 to 48 hours after the activity, though it can happen immediately. This "crash" or "flare-up" can last from a few hours to several months.

Beyond fatigue, patients experience several other distinct physical challenges. Many people suffer from cognitive dysfunction, which is often described as "brain fog." This involves a slowdown in information processing, difficulty concentrating, or trouble finding words. Others experience orthostatic intolerance, which causes dizziness, nausea, or lightheadedness when sitting or standing upright. This can include postural orthostatic tachycardia syndrome (POTS), where the heart rate increases excessively upon standing. Additionally, many patients deal with chronic pain in their muscles or joints, and even hypersensitivity to light, noise, or smells.

Medical experts classify the illness in different ways depending on the observed symptoms. Since 1969, the World Health Organization has classified ME/CFS as a neurological disease. This classification is based on symptoms that suggest the central nervous system plays a key role. Because abnormalities in immune cells are also present, it is sometimes called a neuroimmune condition. Some researchers also view it as a post-acute infection syndrome (PAIS). This category includes conditions like long COVID and post-treatment Lyme disease syndrome, which share similar symptoms.

The history of the illness is marked by significant debate over its name and diagnosis. Many people object to the term "chronic fatigue syndrome" because they feel it trivializes the disease. Others find the term "myalgic encephalomyelitis" problematic because there is limited evidence of brain inflammation. In 2015, the US Institute of Medicine suggested the name systemic exertion intolerance disease (SEID). While the name was not widely adopted, the CDC used its new diagnostic criteria. Reaching a consensus on a single name remains difficult because the underlying pathology is still unknown.

While the exact cause of ME/CFS is unknown, certain patterns are evident. Between 60% and 80% of cases begin following an infection, frequently a viral one like infectious mononucleosis. The illness can occur at any age, including childhood, though it is more common in middle age. It also affects women more often than men. Before the COVID-19 pandemic, the prevalence was estimated at two to nine people per 1,000. However, many people now meet the diagnostic criteria after developing long COVID.

The impact of ME/CFS on a person's life is profound and varies by severity. Severity is often divided into four categories: mild, moderate, severe, and very severe. About one quarter of those affected are unable to leave their homes or beds. In severe cases, individuals may be wheelchair-dependent or entirely bed-bound. The illness can lead to a lower quality of life than many other chronic conditions.

Because there are no approved medications or diagnostic laboratory tests, management focuses on relieving symptoms. One common strategy is pacing, which involves balancing activity to avoid triggering PEM.

ME/CFS is a significant public health issue with large social and economic consequences. It can be socially isolating for those who cannot participate in normal activities. Many patients face stigma in healthcare settings because the disease is not always well-covered in medical training. This can make receiving proper care complicated. Historically, research funding for ME/CFS has been much lower than for other diseases with similar impacts. Understanding the connections between infection, the immune system, and energy production remains a vital area of scientific study.