Oh, I'm so glad you are almost done with your treatment for the cancer! Boxing day is when? December right after Christmas?
Listen, I am sure your health anxiety is truly high and after going through a cancer diagnosis and treatment, that is understandable. It obviously is not good to breath in toxic smoke or smoke with particles in it that could be hazardous to your lungs but generally, when this is an issue, it's prolonged exposure. A one time weekend of being near is unlikely to have repercussions for you. Talk to your doctor about it though. And if you are having more and more anxiety, this truly is something that can be helped for many people. I'd also talk to your doctor too. For a lot of people, it is manageable. But if you find yourself overcome with fear and anxiety often, it is important to speak to a doctor about it.
You're posting on an anxiety forum, not a cancer forum, so my first question would be, is anxiety a chronic problem for you, or are you anxious because you've earned it (cancer makes everyone anxious). You say you sometimes struggle with anxiety, which means it's not really a regular problem, so that probably answers the question, but I just thought I'd ask. As to the burning plastic, worrying won't help. Was it toxic? You bet. Mom's right, usually it takes more than just a brief exposure to cause something like cancer, but it well could have caused something more immediate. But it didn't, so you don't need to worry about it. But I would suggest that, if you get to a point where your treatment is over and you're no longer taking medication and not getting treatments, that you can work on detoxing your system. That would help anything from the plastic fire that might have stored in your liver and also the toxic treatments used to kill cancer cells. What this entails is mostly dietary, which means eating better than you ever ate in your life by loading up on antioxidant rich foods that will help your body recover. It will strengthen your immune system. Some things that are really useful are algae such as spirulina and wheat grass, which is very useful at detoxing your liver, which is where the body stores fat soluble toxins. Lots of green leafy veggies and veggies that have a lot of color -- the color is made by powerful antioxidants. Really high antioxidant foods abound, but some other great ones are rosemary, blueberries, red grapes with seeds, just as an example. This will help you recover from both incidents as much as one can do that. And from now on, stay away from things like burning plastic -- everyone has cancer cells, but they only get us when they're able to mutate and grow exponentially. If you can keep them from doing that, you don't get most forms of cancer. Our world is full of carcinogens, they're in the air, the water, our food, etc. So eat organic if you can, focus on those antioxidant rich foods, and as for the fire and the cancer, forget about them and move on. No sense worrying. It won't help any. Peace.