Fear is one of the four areas in Jim's brain in Earthworm Jim 3D. It has the entrance to the levels Poultrygeist, Death Wormed Up and the battle against Professor Monkey-for-a-Head. There are more two levels, which can be accessed inside the other levels Poultrygeist Too (which is inside Poultrygeist) and Boggie Nights of the Living Dead (which is inside Death Wormed Up).
This sector is based on Jim's fears. Based on the content of the levels, it seems that ghosts, undeads and vampires are the main fears of Earthworm Jim.