  We discuss an extension of the theory of {\em spin-orbit pendulum} phenomenon
given in [1] to relativistic approach. It is done within the so called Dirac
Oscillator. Our first results, focusing on circular wave packet motion have
been published recently [2]. The scope of this paper is motion of a linear wave
packet. In relativistic approach we found {\em Zitterbewegung} in spin-orbit
motion (in Dirac representation) due to coupling to negative energy states.
This effect is washed out in the Foldy-Wouthuysen representation. Another
important change with respect to non-relativistic case is the loss of
periodicity. The phenomenon reminds the time evolution of population inversion
in Jaynes-Cummings model.
