At the time I didn't know I was severely anemic which probably compromised my immune system making me more likely to contracting the flu.
It hit fast. Like others have said, it moves quickly from feeling off to being bed ridden. I think I was in bed for ten - fourteen days. And one of the times I ended up with a post influenza myalgia . . . I literally could barely walk, use my hands . . . all my joints were swollen as if I had arthritis. My dh had gone to work so I phoned my best friend and told her I couldn't get out of bed (and I had three young kids). She came over, took me to the doctor, who told me I had to wait it out. For two weeks I couldn't open jars, turn on taps, etc. I felt like an old lady. I was scared that I would be permanently crippled with theis arthritis. And then I got better.
I have a new appreciation for the flu. It is brutal. (Oh, and arthritis.)
BTW, since taking care of the anemia I have not had a cold or flu. Two years with no illnesses.