It is not uncommon for concussion sufferers to be considered schizoid, which is a personality type (disorder by DSM-IV) where the subject tends to shy from crowds and be more of a loner.

It is also common for personality changes to manifest after a concussion. It all depends on the parts of the brain most effected.

OCD (Obsessive Compulsive Disorder) and other anxiety/panic disorders ( fear of crowds, a subset of agoraphobia) are also common to PCS subjects.

Concussion and other brain injuries tend to magnify personality characteristics. If one is shy, they will likely become very shy after TBI. Angry problems will be magnified. Etc. Talkers tend to become insufferable talkers as they often lose they skills at reading others' reactions.

My mother says that after my concussion at 10 years old, I was not her sweet little boy anymore.