Yours, Etc.: Origins and Uses of 8 Sign-Offs
Old English gidig, variant of gydig "insane, mad, stupid, possessed (by a spirit)," probably from Proto-Germanic *gud-iga-, from *gudam "god" + *-ig "possessed." Meaning "having a confused, swimming sensation" is from 1560s. Meaning "elated" is from 1540s. Related: Giddily; giddiness.