mental illness; emotional disorder
A somewhat literary or formal expression for mental or emotional illness. It is rare; in modern everyday speech, 精神病 or メンタルヘルスの問題 are more common.
He suffered from a mental illness for many years.
Mental illness can happen to anyone.
Compound of 心 (こころ, 'heart, mind') + の (possessive particle) + 病 (やまい, 'illness'). The exact historical origin is uncertain, but it follows a common pattern for forming abstract nouns.