首楞嚴義疏注經 9.266

9.266

受陰未空，前無新證；色陰已盡，歸失故居。前後失准，墮在兩楹，無所依倚，名中墮地。既於此處心無所措，遂生沈憶，以此名修，認為精進。

The aggregate of sensation is not yet empty, so there is no new realization ahead; the aggregate of form has already ended, so they have lost their former abode upon returning. Lacking a standard both before and behind, they fall between the two pillars, having nothing to rely on, which is called 'falling into the intermediate ground.' Since the mind has nowhere to rest here, it sinks into brooding, taking this as practice and mistaking it for vigor.