I keep an aquarium as a hobby, and while cleaning a test tube I suspect I may have accidentally created poisonous hydrogen sulfide gas. Here is the situation: I had a glass test tube that was used about 6 years ago to do nitrate tests on saltwater using a Tetratest Saltwater Nitrate test kit. It was then neglected for about 6 years in storage presumably with some of the test solution intact which may have spilled out or evaporated leaving a layer of gray solid on the bottom, most likely zinc (which was part of the test), but perhaps more than just zinc. I had recalled a demonstration where a zinc penny was dissolved in sulfuric acid, so it occurred to me that I could clean this test tube with some 9.6% sulphuric acid that I had as a pH adjuster for the aquarium. I added the sulphuric acid and observed the zinc layer evolving gas, which I believed to be hydrogen, and at this time there was no odor observed. After several minutes I dumped the contents of the test tube into a sink with running water, at this time I smelled a strong rotten egg sulphur odor which I immediately ran away from and once I stopped I felt dizzy. I immediately left the room and looked up sulphur gas on the internet and found out about toxic hydrogen sulphide gas! I felt dizzy for several hours afterwards, and I thought I was going to die. I thought the reaction I was performing was zinc plus sulphuric acid yields hydrogen gas and aqueous zinc sulphate. According to my research zinc sulphate has no odor so I can't attribute the sulphur smell to it. I imagine there could have been more going on in that test tube than I realized. My question: is it possible that I actually made hydrogen sulphide gas, and if so in any significant quantity to harm myself? I feel foolish for being so careless, and I think I'm alright, but I'd like to understand what happened. I have a minor background in chemistry from my college days, but I am very far from being a chemist! I could use some help to understand this and thank you for your time.