PCS is a frequent cause of depression, regardless of the happiness or sadness in one's life. My psychiatrist explained depression as when the brain gets polluted with the toxic waste from stress. That stress can be from positive life experiences or negative life experiences. We all know how PCS can be an overwhelmingly negative life experience. Add in the lack of social support, physical activity and for a teen, hormones trying to find a balance, and depression should be considered a given.

One of the struggles the PCS brain has is in maintaining the blood brain barrier. Those struggles are why many PCS symptoms show up a few days to weeks after the impact. Immediately after the trauma, the brain tries to strengthen the blood brain barrier. That extra strength does not last long, eventually allowing the toxins to effect the brain. This is when symptoms can start to roar. This same weakening can lead to depression.

This depression-concussion link is well reported even though some neuro psychs try to dismiss it. As discussed in the links posted by Lara, attorney Gordon Johnson warns about this bias held by many neuro-psychs.

But, depression is still not a valid excuse for all of her struggles.