Thank you, @janver06!
You probably have a lot of gunk in your lungs that may make deep breathing difficult for a bit, but that will get better and yoga will help it. I guess you will cough a lot until you can clear that stuff. I highly recommend drinking plenty of water to help flush it from your system, especially if you will also be sweating in yoga. If you get dehydrated, you may get headaches.
Yoga will be very helpful in teaching you to manage stress in a healthy way rather than by reaching for a cigarette. I wish you many blessings on your journey towards health!