Your Question: What is severe COPD?
My Humble Answer: Usually, severe COPD often refers to the last stage of COPD, where your heart is starting to wear down due to working hard to pump blood through your lungs which are severely obstructed. On an X-ray, or CT, this can be seen as an enlarged heart. Usually at this stage you become short of breath with minimal exertion. Now, I don't know if this describes you or not.
To receive the best answer to your question, you should discuss this with your doctor. He should be able to answer every question you have regarding your COPD.