That's damn scary that the airbag deployed for no reason but I don't think BMW owes you anything to be honest (unless you have a VERY good relationship with your dealer). They'll just say well it's out of warranty and have you ever had the airbags/sensors checked, I'm assuming you haven't and boom that's their way out. Also, don't worry about the cough etc, I've been hit with an airbag more than once (always in shotgun) and the worst one resulted in my chest being tight and legs being stiff for about a week. As far as thinking oh I can get money outta BMW, it won't happen either. My engine blew after 5/6 weeks of ownership and when I addressed them with 'my life was in danger' they will immediately come at you with 'are you dead?'
Good luck and let us know how this turns out.