As someone with a family history of mental illness, I try to keep a close eye on my mental state, and it's surprising how much can affect it. Apart from drugs that shouldn't be affecting mental states, even different types of food and how much exercise I get can have noticeable impacts. Those EFA fish oil pills? Not just good for your heart . . .
I try to be aware of biases, but the OTC EFAs were prescribed by my physician, and there have been some studies backing DHA in particular as effective for depression.