Strange replies, i love to smoke when i get sick. I live in north america where the winters are fuckin freezing! So naturally i and everyone around gets a cold or two ever winter. And the first thing i do when i feel it is smoke. Congested? Smoke a fat bong rip and clear that shit out! Feel tired but cant sleep? Smoke an indica and enjoy some nice dreams. achy body and head? Smoke a fatty! Just feeling like shit? Tear up that bong! etc. I mean, it is not going to cure your sickness but it will relieve some symptoms just as well, if not better than otc medication. Surely if you dont agree with anything else you have to admit when you wake up in the morning and cant breath a huge rip will clear that shit out temporarily. Definitely keep in mind that heat and tar are not good for your lungs at any time, so try to stick to bongs and vapes if possible and smoke only what you need to relieve symptoms or you will be a lot more sick for a lot longer.
Shit i forgot to mention about that dry cough thing, if you have serious fits of unproductive coughing while sick do not smoke much at all, if any weed. You will be coughing no matter what but when you have been coughing for a long time it starts to become painful and so coughing harder for a while because of that sweet ganja really hurts and the smoke/tar/heat irritates the lungs/throat more. I have chronic fits of unproductive cough every time i get a cold! It sucks, i cough forever, i can hardly stop long enough to eat and sleep at night is not an option for me or anyone living with me while im sick. Luckily opiates are the one and only thing that can do anything about this, so i get some purple drank from my doctor (codeine cough syrup) and before you know it im leanin like im in a mud puddle and i can finally stop coughing. Any opiate/opioid will be effective for this though, but man its hard to smoke opium when you cannot stop coughing. And once you have the cough under controll your cool to smoke ganj as needed.
peace and good health