My poison Ivy went away very fast?

So i was in the mountains, and i accidentally got into a bunch of Poison Ivy. I started to freak out because i started getting this very red rash and these little under the skin blisters. My grandma went into a store and she bought some water and some medication before taking me to primed. When she got back my rash had already started to disappear, it wasn't as red, and the little blisters started to go down. Within an hour the entire rash was gone. Now i know Poison Ivy doesn't affect certain people, and those people don't suffer a rash. what do you think happened in my case? i checked the leaves to make sure that it was most defiantly poison ivy.