What could I have gotten sick with?

Patient: Hi, I recently experienced the very sudden onset of flu-like symptoms (severe chills, aches and fever), which lasted about 48 hours. As I understand it the flu usually lasts much longer than this. Some posts online seem to say Norovirus (food poisoning) would last that long, but I haven’t had any nausea or diarrhea. Do you know what I may have come down with?

Symptoms: Severe chills, muscle aches and moderate fever

Doctor: