I am assuming you're talking about UK CAA/JAR medical here.
I think it would depend on the cause of vertigo and how long you have been free from symptoms, however you may wish to refer to the following link (JAR medical standards document):-
<A HREF="http://www.jaa.nl/jar/jar/jar/jar.fcl.3.apx.b.c.15.htm" TARGET="_blank">http://www.jaa.nl/jar/jar/jar/jar.fcl.3.apx.b.c.15.htm</A>
You may also wish to telephone CAA Medical Department: telephone number 01293 573686.
They are very helpful and it's worth talking to them (they are normally happy to let you remain anonymous if you wish) before you part with GBP 400 or so for Class 1.