I believe the answer is:
'dizziness' is the definition.
(I know that dizziness can be written as vertigo)
This is all the clue.
(Other definitions for vertigo that I've seen before include "Type of dizziness associated with fear of heights" , "Dizziness at height" , "Sensitivity to heights" , "unbalanced feeling" , "Forty Thieves' password" .)