From Longman Dictionary of Contemporary Englishbogglebog‧gle /ˈbɒɡəl $ ˈbɑː-/ verb → the/your mind boggles, → See Verb table
Examples from the Corpus
boggle• You never boggle at plain-speaking, so why do so now?• The mind boggled, but there it was, every distressing detail.• It boggles my mind how much money it must have cost to set up each base camp.• George went across to introduce himself to the Red Army, an event which boggles the imagination.• The dexterity and nimble balance of elite fencers can boggle the mind.• It boggled the Siberian imagination to think what modern business and technology might accomplish.Origin boggle (1500-1600) Perhaps from bogle; → BOGEY 