There is a lot of chemistry going on with the brain that has to do with the transport of blood in an out of brain tissue. Was reading into some research regarding monitoring of people in stressful conditions. Apparently, when stressed or threatened or in a similar state the body rapidly transits blood from the brain to other areas such as the heart and lungs. Blood flows away from the brain and other areas, like the stomach, and becomes more focused on areas where the body needs to respond rapidly. Consistent and repeated stress will actually reduce and potentially even limit brain function.
If this is true, then you just cannot be constantly in a stressful situation. It will have an adverse impact. Reduced brain function and countless other issues. You have to break the stress up. Meditation, exercise, and other things that can get you to calm down and return the primary functions back to the brain and other non-vital areas.