Striking both of us, undisguised horrific vertigo (9)
I believe the answer is:
giddiness
'vertigo' is the definition.
(I've seen this before)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for giddiness that I've seen before include "State of excitable frivolity" , "Vertigo" , "Excitability and frivolity" .)