Hey there Abbie !
Waves explained it way better than I should had managed too
In my humble opinion, it is more likely that you just get used to "that dosage" of Cymbalta than you havening a major depressive side... Talk to your doc, most of the times, increasing the dosage a little bit will do the trick, or, stopping that medicine for a while just to clean your body and, make it "realise" it actually need that medicine....
You know, I always say our bodies are lazy ones... you give it hormones, and our gladds stop working...

oh well... we stop taking the hormones, and our body realise it has to make our glands work ! haha
So, the same applies for medicines.... our bodies saturate and think they dont need "that" anymore, so, if you stop for a bit, it will work again later on
Take care.