These are the words of our teacher, Patrick Kelly:
“Often people wonder if they should still keep training when ill. Personally I have always kept training and so did my teachers.
Fastest recovery: Research shows clearly that the immune system is enhanced during and after practicing tai ji (where-as the immune system is depressed during and after heavy physical exercise like running, gym work or external martial arts). So continuing tai ji practice is the fastest way to recover.
Worries about being infectious: colds, flus and similar, are most infectious in the few days before obvious symptoms arise, so it is too late to worry about passing it on to others when you feel it the strongest. Also because you have contact with others while their immune system is in an elevated state the chance of their catching it is very much reduced. It may even induce an immune response that offers them protection later when they are in a more vulnerable condition.
Inner Deep Mind versus Outer Superficial Mind: the deep mind receives benefit from the training no matter the state of the body so pushes you to continue. The superficial mind is part of the body (brain consciousness). It has ‘ideas’ about tai ji but can’t really appreciate the true, deep value of training. Superficial mind weakens when the body is ill, then it looses it’s will to continue training, either for a short time or possibly forever.
In your life aim to follow the deep mind (the deep mind is close to the Dao). So we strongly advise you keep training when ill.”