I empathize with your feelings of anxiety and distress. By ASD I am assuming you are referring to Acute Stress Disorder, and yes it does seem by your description that this may be an appropriate tag for your symptoms. There are several ways in which ASD may be demonstrated, and other maladies/disorders that can present with similar symptoms. I heartily encourage you at this time to heed the advice of your mental health professional, who is most qualified to determine which of them may be the accurate diagnosis in your case. Many factors play into a diagnosis - as you know from your own specialty: Neuropsychology. It would be difficult as a professional not intimately aware of the intricacies that make up "Nichole Thomas, RN" to know to how best advise you. What I would however like to share with you are some thoughts/ considerations you may choose to explore in your own self-examination. Do you feel you had done the best you could have under the circumstances, to save this patient? Do you feel that somehow you share in any culpability for the incidents leading to his death? Do you find your self confidence shaken and now cast your own aspersions on yourself? Did the incident cause you to challenge your own beliefs in medicine (a field in which you elected to work to help save people)? Did it cause you to challenge your faith and beliefs about life/death and mortality? It may be of value to consider counselling, and psychotherapies as well as the pharmacotherapies available.
I can tell you this much, you certainly have had an upclose and personal example of how our experiences help shape the "who" we are. What you discern, and proactively do to "pull" yourself out of the distress you now find yourself, will help you more than you may realize in your now and future professional career.
And please remember: Every day we make choices - hopefully the best we can make - being TRUE to ourselves and our core beliefs. In 30 seconds the choices may change, but if we do the best to be TRUE to ourselves, there are no regrets - only growth and learning.
Wishing you the best of health!