expression, i-adjective
have a headache
Literal physical headache. Used as a set phrase describing one's own head pain.
今日は朝から頭が痛い。
I've had a headache since this morning.
二日酔いで頭が痛い。
I have a headache from a hangover.
expression, i-adjective
worrying; troubling; racking one's brains
Idiomatic use: something is a source of worry or mental distress. Often used when a problem is hard to solve or causes anxiety. Compare with 頭の痛い, which can modify a noun directly.
See also: 頭の痛い
お金のことが頭が痛い。
Money matters are troubling me.
彼の将来を考えると頭が痛い。
It worries me to think about his future.