Generally people fear the word Sadesati just like every disease has some medicine so is the case in astrology for every problem there are remedies for people who have exalted saturn have to face less problems in there sadesati compared to others.
Saturn is a slow moving planet and transits every house in two and a half year when it transits one sign before the natal moon in anybodys chart his sadesati begins when saturn transits over the moon in the horoscope that is another two and a half years and the third part is next house after the moons placement that is the last part of two and a half years of the whole sadesati.
An expert can tell u when your sadesati will start and what precautions and remedies u should do there is nothing to fear infact some parts of the sadesati can also reward you. One may have to go and stay in a place far away from home do undesiered travel or loose in business mantra and yantras are of good use at such times we should not fear this phase it comes to teach us something makes us tougher and also makes us humble.
Pic Source: Wiki