Linebackers can be emotional creatures. Maybe the nurse informed him that some of the test were exposing early concerns about the shoulder and he didn't take it well.
I think it's MUCH more likely that he was in a state of anxiety over the fact that he was about to fail a drug test and he flipped his ****.
Either way, screaming "Don't you know who I am?" at a nurse is something that IMO reveals a bit about the individual's character.