Hi, lb --
I'm on Zegerid which is the prescription form of Prilosec, same ingredient but doubled and with sodium bicarb added. I'm usually prone to depression but haven't been feeling depressed at all since I started taking it about two months ago. Just my two cents for what it's worth. Also haven't seen depression listed as a side effect anywhere.
That's not to discount your experience at all! You might have to try getting off of it to see what would happen. These PPIs are weird. I know when I was on Nexium and tried to double my dosage, I started having horrible nightmares, the kind where you wake up screaming because you think your husband's trying to kill you! Whereas he was actually sleeping innocently beside me and woke up totally bewildered by my accusations ...
Hope you figure out the right balance for you.