This word is labeled “colloquial or vulgar” by the OED, so it earns the “low” tag, and the entry for its etymology is too fun not to share:
probably of English dialectal origin; flummock slovenly person, also hurry, bewilderment, flummock to make untidy, disorder, to confuse, bewilder … The formation seems to be onomatopoeic, expressive of the notion of throwing down roughly and untidily; compare flump, hummock, dialect slommock sloven.
In our story, only beloved Bilbo is ever flummoxed.
- 01.058 who was feeling positively flummoxed,
- 01.090 he was so flummoxed.
- 05.014 altogether flummoxed
“flummox, v.” OED Online. Oxford University Press, March 2015. Web. 20 May 2015.