It unfits men for high positions (7)
I believe the answer is:
'it unfits men for high positions' is the definition.
The definition suggests a singular noun which matches the answer.
This is all the clue.
Can you help me to learn more?
(Other definitions for vertigo that I've seen before include "Disturbance in the inner ear" , "attack at altitude?" , "Sense of dizziness - Hitchcock film" , "Sensitivity to heights" , "Whirling sensation when balance is disturbed" .)