The 'unconscious beings', are a class of heavenly beings in the fine-material world; s. deva (II).
"There are, o monks, heavenly beings known as the unconscious ones. As soon, however, as in those beings consciousness arises, those beings will vanish from that world. Now, o monks, it may happen that one of those beings after vanishing from that world, may reappear in this world...." (D. 24).
Further details, s. Kath., Yam. (Guide, pp. 68, 79, 96 ff.).