Believe it or not, the flu can cause pneumonia, an opportune bacteria can take hold while your immune system is preoccupied with another invader. It can also cause 104F fever. I had the same thing the last time I had the flu. About 16 years ago, I was sick for a week. Home in bed. Couldn't get out of bed or do anything. Sweating and shivering at the same time. The fever broke at 3am in the morning. I woke up in soaked sheets and comforter. Got up, changed the sheets and took a shower. Didn't even feel sick any more. That was the last time I was sick. I've not gotten the flu vaccine since. I figured if I was going to get that sick with a flu shot, I wasn't going to bother anymore. I actually thought I was going to die, but I didn't. I don't know what people are dying of for certain, but I don't underestimate the flu any more.