You are not thinking straight. 你现在脑子不清醒，不能清晰地思考。
think straight 头脑清楚地思考，心平气和地想，正确地认为

常用于否定句，表示由于情绪过于高涨或低落、醉酒等原因，不能清晰的思考。

I was so tired, I couldn't think straight.我当时太累了，脑袋都没法思考了

She is too upset to think traight.她太烦躁了，没法理智的思考。

也可以用于肯定句

Think straight, talk straight. 清楚地思考, 并且直言不讳