Becomes unconscious of being old-fashioned (6)
I believe the answer is:
swoons
'becomes' is the definition.
Although both the answer and definition are verbs in their -s form, I can't see how they can define each other.
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for swoons that I've seen before include "Faints as from emotion or heat" , "Keels over" , "Faints, passes out" , "Is listless" .)