see https://www.163.com/dy/article/J079AOTE0543A3A8.html
Some users think it means "you must be crazy (nuts, have your head examined)": 注意 can mean "look out for" see e.g. trainchinese.com, 人在气头上就怕激，1995年盖州市城关镇“8·19”凶杀案侦破始末 or "you better have your head examined"