Mushin is related to egolessness i.e. heijo-shin or muga-mushin, no-self and no-mind.
Both no-self and no-mind have nothing to do with the Western concept of the self and the mind.
For both no-self and no-mind have everything to do with the body and the heart-mind working in unison, in synchronicity i.e. being in the flow.
True mindlessness is when one does which benefits the community with advance preparation but without making a big deal of it.
Anything else is of the negative form of mindlessness.
Mindlessness then means being free of all thoughts of anger, fear, or ego. Likewise, selflessness means not being self-conscious.