Say no whenever you are offer alcohol, drugs, or tobacco.
Even when pressured a simply excuse is a better idea than ruining your life. You see many homeless people that still buy tobacco, drugs, or alcohol and no wonder they are homeless every dollar they get is spent on harmful substances. People use these products to wipe there worries away and do not think about the consequences of tomorrow.
You could try to put cold ice over it to calm down the bruising and then use a cloth and damp it in hot water(warm water) and wipe the bruise properly so that the blood can circulate properly. If you are having troubles breathing then why to relax your muscle, because if you are tense right now it will only make things worse.
And if it really hurt go to the hospital, dont take any risks.