In ancient Egypt, the direction
east was considered the direction of life, because the sun rose in the
east. West was considered the direction of death, of entering the
underworld, because the sun set in the west. They believed that during
the night, the sun traveled through the underworld to make its way
back to the east so it could rise in the east again on the next day.
On the tree of life, note that the
birds representing the first four phases of life all face to the east,
but the bird representing old age faces to the west, anticipating the
approach of death.
Source: http://www.shira.net