Well, this all depends on how bad you feel mate at the end of the day,
1. If you feel that your workout will be of lesser quality then normal, I would personally rest.
2. If you feel you are coming down with something and feel fatigued and go to the gym you may be doing more harm than good.
But then everyone to there own, I would rest.
Why push yourself if you feel ill, especially as xmas is on it's way!