According to one of the doctors, it might be the following reason. In China, the air has some poisonous particles, which are harmful to your body, but they can stimulate the lungs' function.

Another reason might be that you may not be used to the air in Canada.

Or you may be alergic to some material in the air.

Or you spend too much time on computer.

The best way is to exercise more, especially swimming and yoga.