hi Spea,
I have actually no idea why this happens to you. Well I have an idea, but I am not sure.. I just can guess, so don't believe it 100%.
If I equalize not exposed to pressure, then my eardrums are pushed to the outside (overequalizing) and this, especially if prolonged in time, have an impact on your equlibrium center (or in english balance center maybe) located just behind the eardrum (as you certanly know) , and this could imply dizzines.
If you equalize in water (or better underwater) your eardrum is not (shouldn't be) stretched at all and you should not have any problem of dizziness.
BUT as everyone would reccomend, find a buddy or better an experienced group to dive with and try it, no worries. If you are alone then is another story.
Personally I was born in Genova and I used to dive as a kid in the same waters where pionieers such Dulio Marcante, Egidio Cressi, Dario Gonzatti, Ludovico Mares, Luigi Ferraro, made the history of diving. Not that i "absorbed" their incredible experience while in the water, but exposed to the same environment I got what people call the acquaticity (meaning the confidence with water which is not related to swimming for example) as nearly every kid of my riviera gets.
I recently (unfortunately) realized that when you are not a kid anymore, then it is not the same and your preservation insticnt is less active allowing to expose yourself to riscs that could be to hard to handle. But thank God when you are older you have more patience and spending some time in reading you will KNOW what not to do and not just FEEL it as you did when you were a kid. Well this is again another theory of mine, so.. :-/
Contact some diver from your place, meet them, and just try it.. it is not a big deal after all.. if diving was not fun, nobody would do it at all, don't you think?
ciao,
Matteo.