The Cleopatra star was being snapped by acclaimed photographer Rankin for U.K. pharmacy chain Boots in south London when she allegedly fell to the ground.
An ambulance was called to the set and Annis received treatment at the scene, according to Britain's Daily Mail newspaper.
A source tells the publication, "She was definitely a bit shaky once back on her feet. So much so that the entire shoot had to be rescheduled.
"No one was at all sure what had happened, but it was evident she was terribly embarrassed about the attention that she'd drawn to herself."
A spokesman for Annis refused to comment.