How do I deal with seeing someone die?

So, I work in an emergency room and last night i witnessed a death of a guy around my age. I literally saw him die right in front of my eyes, heard his last words ("I can't breathe") and saw him take his last breath. I am having a hard time dealing with it and had a mini anxiety attack as i pulled up to the hospital tonight to work. Now you have to understand my title is a patient sitter. I generally just sit with psychiatry patients as well as alcohol or drug detox's. I was helping a nurse as i often do when I don't have patients to sit for. So now I don't know what to do, I am in shambles.. can anyone help me?