Lincoln without forethought or plan; inadvertently; "came upon the diamond unawares
suddenly and unexpectedly; "rain caught them unawares"; "sorrow comes to all, and to the young it comes with bittered agony because it takes them unawares"- A Lincoln
If something catches you unawares or takes you unawares, it happens when you are not expecting it. Investors and currency dealers were caught completely unawares by the Bundesbank's action The suspect was taken unawares, without the chance to dispose of the evidence