A metaphor describes something by saying that it's something else -- "My girlfriend is a jewel," "His anger was a hurricane," "After the breakup, his life was a barren desert."
An extended metaphor goes into detail about many ways in which one thing resembles another. For example, if you were using a storm as a metaphor for a person's anger, you might say, "His angry face was a sky full of menacing dark clouds. His angry words were a howling wind. The fierce rain of his accusations beat down on us. His threats were thunderclaps and flashes of lightning."
To describe your fear of losing control, you might use being lost in the woods as a metaphor, or being caught in a landslide, or being in a car that's careening along with no brakes. You can probably think of several other out-of-control situations that would also work for your metaphor.
