I watched a program on this...I think it was a UK documentary. I'm trying to find the information for you. They were showing a young girl that had these episodes of passing out...one scene she was just on the street with her girlfriends and she would drop her head and be out of it for awhile. Her friends just treated it as normal and would look after her until she came out of it.
I googled on the term you referred 'seizures' and in one of the symptoms it may be due to genetics. My mother had same type of seizures when she was 10 years old, but they were caused when she was frightened.
But in my brother case, it was happening when he was normal and it was happening after a long gap precisely 6 years back from the latest one. From the health perspective he is doing fine.
Your brother may experience seizures. You should get him to a neurologist and have a head CT or MRI. He may have some serious problems.