"Anyone whose goal is 'something higher' must expect some day to suffer vertigo. What is vertigo? Fear of falling? Then why do we feel it even when the observation tower comes equipped with a sturdy handrail? No, vertigo is something other than the fear of falling. It is the voice of the emptiness below us which tempts and allures us, it is the desire to fall against which, terrified, we defend ourselves."
you could say it's the fear of something immanent in ourselves
quoting Milan Kundera in Unbearable Lightness (chapter end quote)