Oh yeah, you walked into a spawner nest. No wonder you had problems! Next time listen for the sound of flies. That means a spawner is near. You can take them out with arrows, but they will spawn nasty stuff when they are damaged so either proceed with caution, or leave them a lot of room. Usually spawners are in small stone circles or in stone ruins.

If you are very careful you can naked sneak and dash to get your stuff back, or at the very least, move your gear further away from the spawners. I say naked because if your stuff doesn't fit neatly back in your inventory, your best stuff might be left behind, or you may get swatted while messing with the inventory screen. Food and poison potion can improve your chances on a corpse run. Good luck!