Arrived at worked and my stomach was a little upset, but it went away. Then I felt cold. Shortly after, I was freezing, to the point that my whole body was shivering. After that, I got a headache and was dizzy. Then the headache got much worse and I was delirious. Left work, came home and my head was pounding. Checked my temperature and it was 102.9. No cough, sore throat, runny nose, diarrhea, etc. What could this be?