My question: I have earned 10 days vacation and 6 sick days. Can my employer all of a sudden take these sick days away with no compensation, even though they have been earned?

There are no laws requiring employers to provide any paid sick days, so there are also no laws regulating rules regarding their use. I don't see any law that would prevent your employer from taking away your sick days.

In some states, vacation days are treated as deferred wages so that they cannot be taken away. To the best of my knowledge, Mississippi is not one of those states.

Mississippi is not one of those states. While I can't imagine why they WOULD, an employer CAN take vacation or sick days away.