Literally "I think I'm spinning/weaving." This expression conveys disbelief, shock or outrage at something unexpected or unbelievable. Similar to "I can't believe it" or "You must be joking."
The origin is fascinating - "spinnen" (to spin) has a double meaning in German. Historically, spinning thread was tedious work often done in isolation, and people who did it for too long were thought to become eccentric or strange. The phrase plays on this association between spinning and mental instability. In modern usage, it's often shortened to just "Ich spinne!" in casual speech.
🇩🇪 – Als ich die Rechnung sah, dachte ich nur: "Ich glaub, ich spinne! 200 Euro für einen einfachen Haarschnitt?" 🇬🇧 – When I saw the bill, I just thought: "I can't believe it! 200 euros for a simple haircut?"