The spirit of heaviness. What is it? What spiritual weapon is used to defeat it?

(Isa 61:3)  to provide for those who mourn in Zion, to give to them a garland for ashes, the oil of joy for mourning, the garment of praise for the spirit of heaviness; that they may be called trees of righteousness, the planting of Yahweh, that he may be glorified.