Q: Sweet Mother,
Are mental indifference and lack of curiosity a sort of mental inertia?
Usually they are due to mental inertia, unless one has obtained this calm and indifference through a very intense sadhana resulting in a perfect equality for which good and bad, pleasant and unpleasant no longer exist. But in that case, mental activity is replaced by an intuitive activity of a much higher kind.
Ref: Some Answers from The Mother