莫名其妙；摸不着头绪totally confused; head full of fog

• 电影中她还是一贯的满脸迷茫，看得人一头雾水。

  In the film, she had a lost look on her face all the way through. She looked utterly confused.

• 虽然查阅了不少资料，但罗先生仍是一头雾水。

  Although he had checked through many materials, Mr Luo was still totally confused.