Commentary Purg XXXII 70-71

Dante's sleep and awakening in the garden is verbally reminiscent of Ugolino's description of his awakening from his dreadful dream ([Inf XXXIII 27]), the phrase 'squarciò il velame' (the veil was rent) remembered in 'squarciò il velo' (broke my veil of sleep [these are the only two occurrences of that verb in the poem]).  It also reminds us that each of the three previous days on the mountain have ended in sleep and dream.  On this fourth day, which will conclude his experience of the earthly paradise at noon, instead he has this mystic sleep after he has had a final visionary experience of the griffin and his Church.