Nitpicking his condition

If he cant form any new memories, its shown several times that he only remembers for about 30 seconds. Then why does he know about his brain injury, how does he know where he is and whats going on. For example, he's at the dead concert, you'd think that he would be confused, or act surprised and excited. Also, he just sits staring, unresponsive, then he hears his fav music and suddenly he's full of life, talking non stop and acting like a normal person. Very unrealistic imo, and im not even a medical professional