Symptoms after dropping from 30mg to 20mg?

I went down from 30mg to 20mg almost 5 days ago. I am also on Prozac 10mg to help but I swear I feel pretty off. Physically I feel achey and think I have a lot of brain fog. I’m just confused because I did not think going from 30 to 20 was a big change. I am wondering if anyone else has experienced this? Just trying to figure out if what I’m feeling is from the tapering of Cymbalta or something else.