Not definitive as I only knew about creating chloramine gas in this way when there was the TikTok trend of people mixing loads of products in their toilets - however - you would need a high concentration of the gas, somewhere airtight, and an unknown amount of time without any chance of being disturbed as you can be saved from this type of poisoning.
There is also the chance you will end up in a coma rather than it being lethal, so I would recommend doing a lot of research on accidental deaths from this and finding the commonalities between them to increase your chances.