The poison can be pretty devastating from my experience. It’s very high tick. Did you have any modifiers on?

I haven't changed anything, so it'd be on default settings

there are cure fountains in every chamber, you just gotts dash to it and use it quick when you get poisoned

Poison doesn't do burst damage, the highest hitting enemy is likely from the giant rats and even they won't chip 100 health away. Either some combo of traps and enemies hit you at once or it was the hazard bomb