It's likely a misunderstanding or a made-up word.
However, the word could potentially be a combination of "mega" (meaning large) and "strophobia" (meaning fear of rotation or turning).
If this is the case, "megastrophobia" could hypothetically refer to an extreme or debilitating fear of spinning, rotating, or large, swirling objects.
It's important to note that this is purely speculative and not a recognized phobia.
If you or someone you know is experiencing a fear of spinning or rotation, it is recommended to consult with a mental health professional for diagnosis and treatment.