I am sorry to hear that you were diagnosed with lymphoma
. As you well know at this point lymphoma is a cancer involving the uncontrolled growth of certain parts of your immune system called your lymphocytes. Lymphocytes are found all throughout your body as they travel within your blood stream, however they are typically most focused in a system in the body called the lymphatic system.
The lymphatic system has lymph nodes which are essentially stores of lymphocytes that help mount an immune response to an offending agent (usually an infection). As you can imagine, if there are lymphocytes that are growing at an uncontrolled rate (which is basically what happens in cancer), and they normally aggregate within lymph nodes, then if the cancerous lymphocytes set up shop in a particular lymph node it can swell impressively. Typically lymphomas don't grow out of the capsule of the lymph node however, making it unlikely that it actually burst.
However more concerning to me is that you have significant neck swelling and difficulty breathing. Lymph nodes can occasionally swell so large that they push on your airway constricting it which can potentially be a life threatening problem. I would take this very seriously and go get seen by a physician ASAP. If you can see an ENT urgently it would be ideal, however if you feel that your breathing is bad enough, it would definitely warrant a trip to the Emergency Department. I hope that this helps and I wish you all the best.