I am not an ENT doctor, but I think the following diagnoses would suffice to determine each of the conditions:
- Blocked Eustachian tube: Complaints would be of sudden onset and likely associated with a common cold, or ear infection. Providing the patient with standard decongestant should provide quick relief.
- Ruptured eardrum: Patient should have subtle hearing loss apparent on audiogram and it would be relatively easily identified by routine otoscopic examination.
- Perilymph fistula: This condition is hard to diagnose and I quote from Vestibular Disorders Association:
A physician can arrive at a presumptive diagnosis [of a perilymph fistula] through a thorough probing for events close in time to the onset of symptoms, along with a variety of tests. These tests can include hearing tests (audiogram, ECOG), balance tests (VNG, VEMP) and some form of a “fistula test.”
The periplymph fistula is by far the most severe condition and the one with the most prominent effects on the vestibular system (balance). Multiple tests and rigorous medical exam is necessary.
With regard to your presented case study: Again, I am not an ENT doctor but a ruptured ear drum can result in dizziness due to the fact that one inner ear is exposed to cold air due to a rupture and the other ear is not. Unilateral inner ear cooling can result in dizziness. However, blowing your nose is unlikely to cause a ruptured eardrum as it is generally caused by more serious barotrauma (diving accidents and in-air plane cabin pressure malfunctions) (Web MD).
Similarly, the fistula is most often caused by more serious traumatic injuries (Vestibular Disorders Association).
A blocked Eustachian tube sounds the most plausible, as it is associated with the common cold (Web MD). Violently blowing your nose can cause fluid to travel up the middle ear, and possibly cause subsequent infections.