Jedi are very wary of the dark side and sometimes the Sith must also be wary of light side as described in Sean Williams book "Star Wars: The Force Unleashed." People similarly can switch from the dark side to the light side and vice versa although this always has to be triggered by a moment.
The Sith are commonly described to be driven by anger or hate and Yoda puts it along the lines of "Fear is the path to destruction. Fear leads to anger, anger leads hate, hate leads to suffering." So therefore everything we feel is sometimes due to the fears we have and that makes us Sith in some respects.
There is a sense that Jedis are trying to control their extremes by using the force in a fair manner and the Sith use the force to destroy things around them. We are at war with ourselves and others when we are in psychosis and balanced when we take our medication.The Star Wars Saga is very much resemblant to our every day lives and
perhaps why we love it so much. Did you know Carrie Fisher (Princess Leia) is also bipolar.
