Tinnitus

Tinnitus is the perception of noise or ringing in the ear, a common problem that afflicts one in five people. It's not considered a condition itself but rather is a symptom of an underlying condition though usually not a serious one.

Prevalence

 * 2001, In a Belgian study, 48.5% of patients meeting the Fukuda criteria and 52.1% of patients meeting the Holmes criteria, in a cohort of 2073 CFS patients, reported tinnitus.
 * As of 15th May 2018, 78% of 92 members of the patient forum, Science for ME, reported suffering from tinnitus.

Symptom recognition
Tinnitus and "other hearing issues" are a potential symptom of Long COVID in the World Health Organization's definition.

Possible causes

 * cardiovascular problems
 * certain medications
 * ear damage or injury
 * hearing loss
 * potassium channels and channelopathy