Macduff: Look to the lady.

(II.iii.112-113)

Pictured: a woman deviously winking, like she has a secret

Lady Macbeth's faint is her way to distract the men from asking more questions and observing her husband too closely. It’s a completely fake faint, hence the devious wink. This ties into the theme "appearances can be deceiving." This also demonstrates Lady Macbeth’s ambition because she will do anything to succeed.