Make sure you drink lots of water (and electrolytes).
Studies link depression to dehydration because 85% of brain tissue is water.
Dehydration causes energy generation in the brain to decrease.
So my recommendation is to make sure you drink a good amount of water every day to keep the brain fog away.
Because depression is a multi-faceted condition with several causes, involving multiple parts of your body, it would be an overstatement to say that all depression is affected by dehydration. However, in many cases, dehydration could be a contributing factor worth considering.
There is a lot more information to be found about the possible link between dehydration and depression.
You really have nothing to lose and a lot to gain in drinking more water (as long as it is within reason).