That's normal, my first time entering the Swamps was also a culture shock.

Draugrs hit hard if you're in troll gear. I remember sneaking around and clearing them out with my bow until I got enough entrails to make sausages. After that, life in the Swamps got slightly easier.

Like what others said, you were eating starter-level food into the 3rd biome, which was mostly likely the cause of your death. Try eating proper food (i.e. those cooked using the cauldron) from the previous biome if you're entering the next biome for the first time.