Possible meth lab?

I live in a 3rd floor apartment and I am suspicious about my neighbors below me. Its three people in a one bedroom apartment and on the weekends, they never leave and I can hear them coughing and gagging all the time, but I never smell smoke, so I don't think it's weed. I overheard two of them talking about calling one of their dealers (I used to be a big pot head in high school so I'm not oblivious to what they were talking about.) They have their windows covered with blankets and my biggest red flag is that I noticed they have a bunch of small propane tanks (like the kind you take camping) sitting out on their balcony. They do have a gas grill, but it's my understanding that full size grills do not have attachments for those little tanks. Do I have a reason to be concerned? Oh and also, since I've moved in here, I've been sick non stop. I'd hate to be wrong, but of course I'm concerned about my health. How can I anonymously voice my concerns? Who should I talk to?