On Thursday, 9/2/2021, I purchased a 20-oz. bottle of Diet Coke (NOV121UVB1946) at a sandwich shop in South San Francisco, CA. When I opened the bottle, it had a normal smell. By the time I reached the middle of the bottle, not only was there a rancid smell, the Diet Coke had developed a weird taste. Shortly after, I became nauseous and sleepy; it took several hours to recover. On Monday, 9/5/2021, I purchased another 20-oz. Diet Coke (NOV2221UVD0015), this time at a Safeway in San Mateo, CA. When the bottle was opened, again, it smelled normal, and again, by the time I reached the middle of the bottle, there was a rancid smell - like a bacteria infested sponge - only this time, there was no issue with the Diet Coke drink. I have read about numerous issues with Coke Zero, but this is DIET COKE.