What has happened to me???

Ok, I have never once been in a fight. Nor have I got punched in the face with full force. Well heres what happened, I was listening to music while working on a project in class. Then this guy grabs my headphones so I quickly grabbed them back and said "Stay off." in a stern voice. He then slaps me on the backside of my head so which I stand up from my chair and say "Back off!". He decides to punch me but I tried to block and dodge his hits but ended up getting punched in the face with a bloody nose. After that punch, the teacher sent him out in the hallway and I just immediately sit down and literally dont even remember what happened so I tried to find my bearings. Later that day, I felt different, I had someone weird feeling going on throughout my heart. I don't know what it is. Is it confidence? Or is it something else? Can anybody explain this to me please?