While “flustered” is within the Hundred Thousand, the singular noun “fluster”, as we have in 02.004, is not.  In addition to its current use, “fluster” has an obsolete use which indicates that the agitated state of mind stems from intoxication.

• 01.024 Yesterday he had been too flustered to do anything of the kind.
• 01.033 but they have begun to arrive had flustered him badly.
• 01.138 and he was so flustered that he answered
• 02.004 in a fluster.
• 05.047 he was so flustered by the egg-question.

“fluster, n.” OED Online. Oxford University Press, March 2015. Web. 1 June 2015.