It's a common misconception that the self and the brain are one and the same. Not so. The brain is a very complex and capable computer. The self is the user. There are aspects of the way the computer functions that make it very efficient, but can also lead to poor judgments and decision making if one is not aware of them. One to be very aware of is rationalization.
The brain doesn't like uncertainty or not knowing. It wants an answer and it wants one now. It will make one up if it has to. If you suddenly experience fear, the brain wants to know why. The emotion is supposed to give the brain a heads up to something that has changed in the environment or situation. If you look around and take stock of the situation and there is no obvious answer, the brain will move from facts to possibilities and it will keep piecing bits of data together until it has something plausible.
The problem is the brain will find an answer whether the alarm bell was legitimate or not. If you're experiencing fear or anxiety due to a chemical imbalance and not due to any real danger, your brain will find something for you to be afraid of. It works the same with depression. If you're in depressive mode your brain will make mountains out of molehills for you and give you something, many things, to be depressed about.
Awareness is your counter-measure. Objective, logical analysis is your best tool. Your brain and your emotions are your advisers. You are the boss, or at least you're supposed to be. If you've been derelict in your duties, take back the reigns and get back to driving.