Is this a sign of mental illness or is it the bondage of our karma?
Saturn’s influence over Moon will bring mental stagnation. The mind will keep hovering over specific memories (mostly about failures). This preoccupation will dampen the native’s motivation and will cause a lack of interest in his job.
But, as you have mentioned Saturn’s influence also means to bear the burden of a job or even family. Here the innate strength of the native is to be ascertained by understanding the other planetary positions, especially that of the ascendant lord.
If the person is skillful and experienced then with all the worries the person would be able to do his work too, but if the person is not skilled and has little experience then the native will suffer in his work performance and go through a bad time.