Traditionally, Yuzu fruits are used in a hot bath on the day of the winter solstice (Toji) to ward off a range of winter ills, such as colds and flu. To make a 'Yuzu yu' (Yuzu bath), the whole fruits are added and squeezed in the hot bathwater, or yuzu juice or just the peel are added, and just as in aromatherapy, a nice long relaxing soak would bring about a feeling of wellbeing.
Of course, yuzu baths can be enjoyed at anytime for other conditions such as arthritis, rheumatism and general aches and pains. The oil from the fruit produces a tonic effect that stimulates the circulatory system and digestive system...It is a very effective oil for use with stress, burn-out, nervous tension or anxiety, where it helps to bring a soothing and calming effect to the emotions. Likewise it gives upliftment to depressive states, frustration, regret and also helps to build confidence. ~ from here.
Yuzu is hard to find here in Canada - I've looked for a sauce I was making before.. to get a similar effect you could use other citrus fruits - I am going to use a few mandarin oranges and a grapefruit. : )