expression, godan verb (-su)
to fatigue one's mind; to mentally exhaust oneself
Describes the act of tiring out one's mind, often through worry, overthinking, or mental strain. The verb 疲らす is a less common transitive form of 疲れる; the more usual expression is 心を疲れさせる.
彼は細かいことを気にしすぎて、心を疲らしてしまった。
He worried too much about small things and fatigued his mind.
More common and natural way to express 'to fatigue one's mind'. 心を疲らす is a rarer, somewhat literary variant.
Compound of 心 (こころ, 'mind') + を + 疲らす (つからす, transitive form of 疲れる 'to become tired'). The verb 疲らす is a rare transitive counterpart; the exact derivation is uncertain, but it follows a pattern of forming transitive verbs from intransitive ones.