The Collaborative International Dictionary of English v.0.48:

Vertigo \Ver"ti*go\ (?; 277), n.; pl. E. Vertigoes, L.
   Vertigines. [L., fr. vertere to turn. See Verse.]
   1. (Med.) Dizziness or swimming of the head; an affection of
      the head in which objects, though stationary, appear to
      move in various directions, and the person affected finds
      it difficult to maintain an erect posture; giddiness.
      --Quain.
      [1913 Webster]

   2. (Zool.) Any one of numerous species of small land snails
      belonging to the genus Vertigo, having an elongated or
      conical spiral shell and usually teeth in the aperture.
      [1913 Webster]

WordNet (r) 3.0 (2006):

vertigo
    n 1: a reeling sensation; a feeling that you are about to fall
         [syn: dizziness, giddiness, lightheadedness,
         vertigo]

Moby Thesaurus II by Grady Ward, 1.0:

80 Moby Thesaurus words for "vertigo":
   abscess, ague, anemia, ankylosis, anoxia, apnea, asphyxiation,
   asthma, ataxia, atrophy, backache, bleeding, blennorhea, cachexia,
   cachexy, chill, chills, colic, constipation, convulsion, coughing,
   cyanosis, diarrhea, dizziness, dropsy, drunkenness, dysentery,
   dyspepsia, dyspnea, edema, emaciation, fainting, fatigue, fever,
   fibrillation, flux, giddiness, growth, hemorrhage,
   high blood pressure, hydrops, hypertension, hypotension, icterus,
   indigestion, inflammation, insomnia, instability, itching,
   jaundice, labored breathing, lightheadedness, low blood pressure,
   lumbago, marasmus, nasal discharge, nausea, necrosis, pain,
   paralysis, pruritus, rash, rheum, sclerosis, seizure, shock,
   skin eruption, sneezing, sore, spasm, spinning head, swimming,
   tabes, tachycardia, tumor, upset stomach, vertiginousness,
   vomiting, wasting, wooziness