Frank J. Wilstach, comp. A Dictionary of Similes. 1916.

Unaware

Catch Truth and Reason unawares,
As Men do Health in wholesome Airs.
—Samuel Butler

Unawares, like the stroke of sudden death.
—Nathaniel Hawthorne

Great thoughts, great feelings come to them, like instincts, unawares.
—Richard Monckton Milnes