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.
 * 2018, 78%, as at 15th May 2018, of 92 members of the patient forum Science for ME reported suffering from tinnitus.

Possible causes
Tinnitus is described as involving potassium channels and channelopathy.