Japanese with Manga

Becoming lightheaded with

気(き)が遠(とお)くなる literally means “one’s spirit becomes distant”. It can describe feeling faint or losing consciousness. Figuratively, it also describes being overwhelmed by an exhausting or astonishing prospect.

Dictionary Definition

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

Further Reading

Examples

Dazed by a wristwatch with 気が遠くなる

Learn the meaning and usage of the idiom 気が遠くなる in Japanese, with examples from manga.
美少女戦士セーラームーン » Volume 6 » Page 264

At the stroke of midnight, Chibiusa wakes to a mysterious glow from her new wristwatch. She gets out of bed in a daze, and begins to leave the room. Her cat, Diana, bites her on the arm, returning Chibiusa from her trance.

ちびうさ:
「この腕時計(うでとけい)見(み)てたら気(き)が遠(とお)くなったのよ〰〰」
“When I looked at this wristwatch, I became lightheaded〰”
「ダイアナ！　ヘンよ　この時計(とけい)！」
“Diana! Something is strange about this watch!”
「とにかく　一(いち)の橋(はし)公園(こうえん)へ行(い)ってみましょ！　スモール・レディ！！」
“Anyway, let's try going to Ichinohashi Park! Small Lady!!”