I'm trying to recall a short story I read in the late 60's. It's about a man who "dreams" that he is slowly being consumed by ant-like creatures while he sleeps. Consumed is probably not the right word - more like replaced, bit by bit. Then one night, as he lies paralyzed in bed, he sees himself enter the bedroom, open a briefcase and summon all the ants . He watches in horror as his own body slowly disassembles into the ants and then crawl into the briefcase. The copy of himself, picks up the case and walks out. Any ideas ?