1876, from German Grübelsucht, psychiatric term for "a form of obsession in which even the simplest facts are compulsively queried" [OED], from grübeln "to brood" (see grub (v.)) + sucht "mania."
Entries linking to grubelsucht
grub v.
c. 1300, "dig in the ground," from hypothetical Old English *grybban, *grubbian, from West Germanic *grubbjan (source also of Middle Dutch grobben, Old High German grubilon "to dig, search," German grübeln "to meditate, ponder"), from PIE *ghrebh- (2) "to dig, bury, scratch" (see grave (n.)). Transitive sense "dig up by the roots" is from 1550s. Related: Grubbed; grubbing.