A condition defined by substantial fatigue plus other symptoms, often including post exertional malaise (symptom worsening after activity), unrefreshing sleep, and cognitive issues. Severity ranges from mild to profoundly disabling.

A symptom, not a diagnosis. “Chronic fatigue” describes ongoing low energy that can have many causes. ME/CFS is one specific diagnosis within a broader fatigue landscape.

Persistent symptoms that continue or appear after COVID 19 infection. Presentations vary and may include fatigue, exertion intolerance, autonomic symptoms, sleep disruption, cognitive issues, pain, and more.

A condition where mast cells release mediators inappropriately, potentially causing multi system symptoms like flushing, hives, GI issues, headaches, blood pressure swings, and reactions to triggers. Diagnosis is nuanced and often confused with other causes of reactivity.

An umbrella term for dysfunction of the autonomic nervous system, which regulates heart rate, blood pressure, temperature, digestion, and more.

A condition where heart rate rises abnormally with standing, often with lightheadedness, fatigue, brain fog, palpitations, or exercise intolerance. Causes and subtypes vary.

Symptoms that worsen when upright and improve when lying down. Can include dizziness, weakness, nausea, palpitations, and cognitive slowing.

Persistent symptoms following an infection that last beyond the expected recovery window. Long COVID is one example; other infections can lead to similar patterns.

A pattern where the nervous system becomes more reactive and amplifies input. People may become more sensitive to pain, light, sound, exertion, stress, or stimulation. It is a physiologic pattern, not “imagined.”

A condition where brain network functioning leads to real neurologic symptoms (movement, sensory, speech, gait, etc.) without a structural lesion explaining them. It is not malingering and requires careful evaluation.

A condition characterized by widespread pain and tenderness, often with fatigue, sleep disruption, and cognitive symptoms. It commonly overlaps with autonomic symptoms and sensitization patterns.

Frequent migraine attacks that can include head pain, light sensitivity, nausea, vertigo, and cognitive symptoms. Autonomic and sensory regulation can play a role.

A disorder of small nerve fibers that can cause burning pain, tingling, numbness, temperature dysregulation, sweating changes, and autonomic symptoms. Diagnosis usually involves specific testing.

A term used when people notice symptoms after histamine rich foods. It may relate to multiple mechanisms and is not the same thing as MCAS. The label is commonly used but often oversimplified.

A popular label, not a formal medical diagnosis. People use it to describe exhaustion and stress intolerance. True adrenal insufficiency is a different, diagnosable condition.

Terms used to describe multi system symptoms attributed to mold exposure. The topic is debated and definitions vary. Regardless of label, people’s symptoms are real and deserve careful evaluation.

Some people have persistent symptoms after Lyme disease treatment. Terminology and mechanisms are debated. It often overlaps with fatigue, pain, and neurologic symptom patterns.

Inflammation related processes affecting the nervous system. The term is often used loosely. In research, it usually refers to specific immune signaling and glial activation patterns.

Variation in time between heartbeats. It can reflect autonomic state, but it is noisy and affected by sleep, illness, training, stress, and measurement method. Useful for trends, not single numbers.

Worsening of symptoms after physical or cognitive activity, often delayed and disproportionate to the effort. It can last days or longer and is a key concept in ME/CFS and some Long COVID presentations.