Can you clarify what the person describes when reporting "dizziness". How long is the duration, how quick onset, body/head positions to agg/ease etc. Is it true-vertigo (rotational spinning of room or person) or non-vertigo dizziness (light headed, unsteady etc) ? If its true vertigo then its unlikely to be cervical in origin. Are there any other symptoms present e.g. tinnitus/HA/nystagmus etc?.

C5-6 seems a little low for reproduction of classical articular cervicogenic symptoms and an accurate upper Cs quad should be positive if cervical in origin.