Strange behaviour

There was a sudden plan and our family went out on car. I was really excited as it was our new car, and we went on a long drive on my birthday, we were six members, we were all enjoying singing, laughing, cracking jokes. But my brother was quite all the way looking outside with a spark in his eyes. He was specially challenged but our beloved. He suddenly told to stop the car as he came across something. He came out quickly, as if he was trying to remember something, speaking single words in every second. We couldn't understand anything, he mumbled a few words again and we told him to go inside the car. We halted near a restaurant, Father packed some food for us. My brother was little disturbed, we were going one by one to him and getting him involved in various topics. It seemed it was not the same boy as he was before. He had changed suddenly. We called the doctor, he sat quietly on the bed, at times not recognising himself, he looked around at the things with a blank stare, the doctor told to take special care of him. He prescribed some medicines and told not to panic, I told my father to think calmly, so he talked to the doctor and I just went on noticing he nodded to the every word, and comforting me, but he told me later he couldn't understand the critical medicinal words. I asked, "Dad, something very serious?" He was going to say something but my aunt interrupted, as if trying to stop him. I couldn't understand the reason of doing so, I ignored.