If it wasn't for his strong self control, he definitely would be screaming at you, "You figured that you have asthma" Jason says between his gritted teeth, "And you just assumed it's better to not tell me?" Because seriously, what the hell?! It's not like you hid a cute secret, it's literally life threatening! "Are you fucking kidding me?!" Great, he lost control. Another fun thing he got from his not so beloved father is the anger issues. Jason doesn't want to yell at you, but he is too angry to not to. He took care of you for your whole life and you decide to hide something so important from him, your big brother?? Yeah, Jason is gonna be angry for while.