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It sounds like your brother has a very serious problem. Not wanting to be alone around unknown people could be social phobia. He can try the BrainPhysics online Social Phobia test at http://www.brainphysics.com/social-anxiety-test.php. However, unless your brother was a child, screaming around people is unusual, and losing memory even more so.
I would suggest seeing a psychologist or psychiatrist immediately. Social phobia is best treated with cognitive behavioral therapy. With an in-person interview, a mental health professional can better determine what the other problems are.
Best of luck,
Dr. Williams
Monnica T. Williams, Ph.D., Clinical Psychology
No Cost OCD Treatment: http://www.ocdproject.org