τὸ δ' ἐξαίφνης τὸ ἐν ἀναισθήτῳ χρόνῳ διὰ μικρότητα ἐκστάν → suddenly refers to what has departed from its former condition in a time imperceptible because of its smallness
undĕcĭes:
I num. adv. unus-decies, eleven times: hanc summam undecies multiplicato, fiunt, etc., Col. 5, 2, 7: surrexi unā cenā, Mart. 5, 79, 1.