Okay, first off, I do not suffer from olfactory or any other type of hallucinations.
I just came down with a cold last week, and this afternoon I had the same experience I had a number of years ago, also during the time of a cold. Today, when I opened the door of the balcony to shoo a pigeon away, my lungs took in one gulp of a horrible smelling chemical that I could not identify - a cross between chlorine, ammonia and something else I can't identify. It took my breath away. When I left the apartment shortly thereafter to run an errand, the smell was overpowering in the hallway and outdoors, even at my destination, which was miles away. I had to put my hand over my nose and mouth. Of course, everyone was acting quite normally and the few people I ventured to ask didn't smell anything. When I got home I eventually recovered and called a tele health number. The nurse, at least, believed me and did not think I was crazy. She actually suggested the paramedics but I said I would go to Emergency once I got mom settled. Which I didn't, but I am definitely going to follow up. I don't know if I'm developing some kind of asthma from environmental triggers or if my body is producing its own chemicals that are interacting with those outside because of my cold. I am convinced there's a logical explanation to this, lol.