Food is a funny thing. It feeds and nourishes us, but it can also harm us. If I prepared the food and set some aside for myself, I would eat it. If the food was plated for a banquet and never served to a customer, I would eat it. If that same food was served to a customer and looked like it had not been touched, I would not eat it. I would never eat anything that had been served no matter how much I thought it was still edible.
Food can harbor unseen pathogens. Once food has been served, it should be considered contaminated and unsafe for anyone to eat except for the person it was served to. Unless you personally watched that plate go untouched the whole time and you never looked away, that plate should be considered unsafe for you to eat it.
Are you taking any medication for your sinus infection? If so, perhaps your sinus medicine is also therapeutic for your ADHD?