Greetings Precious,
There may be a variety of sensations as the lungs and body adapt and balance to a new way of doing something and the opening of channels.
How are you breathing during the exercises? Chunyi usually recommends just breathing in a relaxed, even way when first learning the work, and then adding the reversed breathing when you are comfortable with the exercises and mediations.
And as always, he mentions to check with your doctor before starting and new exercise program.
Much Love, Shawn