The numerous symptoms of ME/CFS vary among individuals and even in the same person over time. Symptoms include but are not limited to: debilitating fatigue, post-exertional malaise, especially following minor activity, sore throat, cervical or axillary lymph node enlargement, new onset of headache, myalgia (muscle soreness or pain), arthralgia (joint pain but no associated swelling), sleep disorders, unrefreshing sleep, cognitive dysfunction, low-grade fevers and night sweats; chest pain, sensitivities to noise, light, foods, medications and chemicals, gastrointestinal symptoms, depression, mood swings, and decreased libido (sex drive). Exposure to multiple sensory inputs such as noise, motion and sound can lead to sensory overload, irritability and relapse. Weight gain is common. Prolonged relapse of symptoms often occurs after simple viral or bacterial infection, emotional stress or exercise. Vaccination can cause self-limited, mild relapse in about half of the patients.

Symptoms often improve when patients become pregnant but could get worse about 6-8 weeks after delivery.