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The vivid dreams are a very common side effect of the SSRI medications (the class of meds that includes Cymbalta). It is also fairly common to have dizziness and fogginess as you're weaning off of these meds- usually it helps to slow the weaning process if the symptoms are interfering too much with your life. But I would certainly consult your doctor if these symptoms persist or become worse.
Certainly if the symptoms become unbearable, going back up to the original dosage of Cymbalta is one way to make them stop. But if you're trying to wean off, that might make the process take longer. Using a shorter-acting drug like Xanax or Klonopin can help manage any anxiety that comes up for you during your withdrawal process but probably won't stop the vivid dreams. In my experience, the dreams return to normal once you're totally off of the Cymbalta for about a week or two. Using one of these other meds like Xanax or Klonopin might make you so sleepy that you sleep in spite of the dreams, but I'm not sure they would stop them.
Given how much trouble you're having with this withdrawal, I would strongly recommend that you discuss these issues with the doctor who prescribed you these meds in the first place to get his/her suggestions.