Becoming lightheaded with 気が遠くなる

意識(いしき)がなくなる。正気(しょうき)を失(うしな)う。

To lose consciousness. To lose one's sanity.

Goo Dictionary

気(き)が遠(とお)くなる means to become lightheaded, to feel faint, or to be overwhelmed. Your 気 (spirit) does the action of 遠くなる (to become distant) from you. It can also mean to faint or pass out.

Examples

Dazed by a wristwatch with 気が遠くなる

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