Final answer:
The next test to be ordered should be Audiometry.
Step-by-step explanation:
The patient's symptoms, including sudden onset dizziness, spinning sensation, ear fullness, tinnitus, and fluctuating hearing loss, are indicative of Ménière's disease, a disorder that affects balance and hearing. Given the symptoms, the next test to be ordered should be Audiometry, which measures the patient's hearing ability. This test will help assess the extent of the hearing loss and provide valuable information for diagnosis and treatment.