It involves smelling four essential oils - rose, eucalyptus, lemon, and clove were originally recommended – twice a day for a few minutes. But adding different odors - as well as objects like rubber bands and crayons - to the aroma arsenal may help awaken the brain, Kelly said. The key is to focus on the smells; don't try to read emails at the same time.

Keep training, and track your progress.

— Workshops at the Monell Chemical Senses Center in Philadelphia try to "retrain" people who have lost their sense of smell. Read more at When the nose doesn't know: Recovering lost sense of smell at Philly.com.