verb

disturb the composure of; unsettle.

the abrupt change of subject disconcerted her

unsettle,nonplus,discomfit,throw/catch off balance,take aback,unnerve,disorient,perturb,disturb,perplex,confuse,bewilder,baffle,fluster,ruffle,shake,upset,agitate,worry,dismay,put out of countenance,discountenance,discompose,surprise,take by surprise,startle,stop someone in their tracks,distract,embarrass,abash,throw,faze,discombobulate,rattle,psych out,cause to be at a stand,gravel