letter of complaint

It never occurs to me that I will ever receive a letter of complaint from patient for poor services, and worse still for being negligent.
Was I negligent in my care, in missing a diagnosis and as a result rendered the patient in a worse situation? Or was it just an unfortunate case of poor response to treatment given, and delayed diagnosis?
Even though my conscience is clear, the thought of on the receiving end of the complaint still bothers me a lot.
When I first heard about the potential complaint, and the negative words uttered by the parent (effectively alleging that I was incompetent and had been negligent in my care), I was very disturbed.
When I heard that the parent was going to or had filed a complaint to "Ministry", my trend of thoughts/focus was severely disturbed. I was effectively thrown into a state despair for the next few days.
I have to dwelve into the details of what transpired when the patient was under my care, to counter the various allegations made by the parents, and attend hospital meeting to defend my case.

All was quite for a few months, until I received an official letter from SMC just one month ago, asking me to submit a written explanation to the complaint filed by the parent.

The final version of my former reply was finally done and submitted to SMC today... lets pray for the best!

Final update in March 2019 - was finally cleared of any wrongdoing by the Complaint Committee; but was advised to better communicate with parents/patients in the future.