I have also noted that in the presence of bradycardia and hypotension, 5 -10 mgs of IV ephedrine easily reverses symptoms. (Of course, if the dexmedetomidine is the culprit)
I have been using dexmed infusion for sedation and analgesia in mastoid surgery. Whenever there is brady or hypotension (often encountered) I almost always reduce the rate of infusion for the time being until the desired level of hemodynamic stability is reached(often needed in those surgery).