@sclerobro , hello, old boy (he says, tongue-in-cheek!). 😉
I would identify these as two different problems. Brain fog is a cognition problem, associated with MS. Our brains have to work overtime, trying to interpret those neural messages that are travelling over our MS damage. As a result, we can be mentally tired and have problems recalling things that we know.
Likewise, dizzy spells are a form of vertigo. There can be many causes, including MS. It’s wise to consult your GP to eliminate any non-MS causes.