Is it okay to workout if you are sick? You work hard every week to maintain your physique and you don't want to lose all the progress you've made, so can you still hit the gym when you are ill? Conventional wisdom would say 'probably not', but the real answer is that it depends.
If you want to know if it's okay to take a spin class or strike a yoga pose, check your symptoms. As PictureFit states above, you can use the "Above/Below The Neck Check" to determine if you are okay to workout. Symptoms above-the-neck, such as a Light Sore Throat, Nasal Congestion, and Coughing are usually okay to test. Below-the-neck symptoms, like Chest Congestion, Fever and Vomiting mean you should stay home and rest.
All of this of course is based on how you feel and if you don't think you are capable of making a workout count, then sit it out. If you do decide to workout, make sure that you get outside or try a home workout, because you don't want to have your whole gym come down with something.
Also keep in mind that if your are feeling bad, many people report that a workout makes them feel a bit better, at least temporarily. You can always dial down the intesiity to make the effort more managable. In addition, if you are just have a bad day, exercise is great for your mental health. So don't let a little winter cough hold you back, get out there and work.