I was in a cycling class the other night and there was a woman on a bike next to me who was clearly suffering from a bad cold. She had a wad of tissues tucked in her bike shorts and she kept blowing her nose and coughing. At one point I asked her if she felt okay, and she said, no, she felt terrible, but she didn't want to miss her workout. I'm sorry, but that's insanity. For one thing, she was spreading her germs, and she was also failing to give her body a much-needed rest to recover from the virus she was obviously dealing with.
One of our HerWriters just wrote on this very topic, and her article can be found here: https://www.empowher.com/news/herarticle/2009/02/20/are-you-too-sick-workout
Although she does mention in her article that it's okay to workout when you're suffering from certain symptoms, I still think it's better just to forgo it till you're back to 100%. Why tax your body further when it's trying to recover?