be hot and cold

1. To feel that one's body is both hot and cold at once, as from shock or illness. After the pneumonia took hold, she was hot and cold all night. I was suddenly hot and cold all over when I remembered how that dog lunged at me. I was hot and cold as I watched the truck swerve into my lane—and then everything went black.

2. To alternate between two opposite states, especially being enthusiastic or interested one moment and disinterested the next. He was hot and cold throughout our entire date, so I have no idea if he wants to see me again. The boss has been hot and cold about whether or not we're going through with this project. I wish she would just make a decision. A: "So, how are things going between you and Mallory?" B: "Hard to tell. She's hot and cold one day to the next, so I can never tell how she really feels!