Hadal

On the surface of the seas, the fear and dread which questions what vast and mysterious beasts lurk beneath you is known as Thalassophobia. At the bottom of the sea, the pressing weight of the miles of dense, dark water above your head and all the unfathomable leviathan it contains, held back only by the pressure of your capsule, is known as Claustrophobia. Travelling down from one to the other brings out the worst of both worlds. What then, I wonder, is the name for that same dread when felt at the bottom of the ocean when one realises that this is not the bottom of the ocean?
The vast is far deeper than we ever knew. I cannot begin to comprehend the behemoths within it.