Insane brother threatens murder.Am I in danger?

Hi, my family is currently in NY because my sister and I have an acting audition. I have to share a room with my brother. I want him to turn the sound off his computer so I could Practice and he wouldn't so I flipped out on him to the point of throwing him and twisting his arm. Now I'm not crazy, I just snapped because he is the most insulting person I know and has done nothing but make this trip hell for my family and insult me, not to mention this audition is important to me. Now somewhere along the line he threatened to stab me in my sleep. He has only threatened this once before when he was 8 or 9. He has mental problems,I'm pretty sure he is bipolar but my parents are iffy. I believe he is also a psychopath. My mom is a therapist but she just met up with some old friends and is to drunk to help. My step dad is very laissez and says dont worry about it. I just think they are blind because it is their child. I'm asking you guys, do you think i should worry?