An adjective describing being driven nearly mad by intense emotion (grief, love, etc.); a strong, often literary expression.
彼のことを思うと胸が狂おしいほど痛む。
When I think of him, my chest aches as if maddening.
別れの知らせを受けて狂おしいほど泣いた。
I cried as if driven mad when I received the news of the parting.
その歌を聴くと狂おしいほど懐かしい感情が湧く。
Hearing that song fills me with nostalgia to the point of madness.