Are you talking about a houseplant?

Deni, you are right, it is overwatered, if it is in a pot, knock it out of the pot and lay it on an old newspaper with a sheet of polythene underneath. Turn it after 12 hours, leave for at least a day in a warm place. Pot up again in a large clay pot.

Where in the world are you, Deni? If you are in Australia or South Africa, Arum Lilies go dormant in the hottest part of the summer. In some parts of the northern hemisphere--southern France, central Spain, Northern Italy, etc.--they may just now be going dormant for the winter