The fifth day of the Saturnalia coincides with the festival of the goddess Angerona, called the Divalia by some and the Angeronalia by others. One explanation for the origin of the name goes something like this:

"The festival of the goddess Angerona who was named from the disease angina because she had once prescribed remedies for it. They set up a statue of her with her mouth bound on the altar of Volupia, in order to warn that no one should communicate the secret name of the city."

Whether or not Diva Angerona was the goddess of the secret name, her own name and her nature were disputed among the Romans themselves. Some connected her name to angina or angor. She gave relief from pain of disease or from worry of mind. (According to Macrobius, she was represented with a finger on her lips.)

Shhh! I personally think that widespread hangovers had a lot to do with this observance...