The same thing happens to me with Crohns. I feel like I have the flu and feel achy and weak and start to shiver. Then I wake up soaked with sweat during the night. After the fevers go away, I am tired for days. Sometimes it lasts a day or two and somtimes longer.
I also was on Humira for 9 months last year but quit taking it when I developed an abscess in my colon.
This is the scary thing that I want to alert you to. I was sick with fevers, loss of appetite and pain in my side for weeks but my white blood count stayed in normal ranges. It wasn't until I was rushed to the ER that a CAT scan showed the abscess and then I was treated for the infection. I am sure that in my case, the Humira somehow affected my WBC and doctors don't dispute it when I mention it to them. They couldn't explain the test results and were just relieved when the infection was finally diagnosed and they were able to treat it. What works great for one person can be harmful to another, so I am avoiding all of the biologics now.