Old English sorg "grief, regret, trouble, care, pain, anxiety," from Proto-Germanic *sorg- (source also of Old Saxon sorga, Old Norse sorg, Middle Dutch sorghe, Dutch zorg, Old High German soraga, German sorge, Gothic saurga), perhaps from PIE *swergh- "to worry, be sick" (source also of Sanskrit surksati "cares for," Lithuanian sergu, sirgti "to be sick," Old Church Slavonic sraga "sickness," Old Irish serg "sickness"). Not connected etymologically with sore (adj.) or sorry.
Old English sorgian, from sorg (see sorrow (n.)). Related: Sorrowed; sorrowing. Compare Dutch zorgen, German sorgen, Gothic saurgan.