You're a master of Occlumency, the act of blocking legilimency. Whenever someone even tried to access your thoughts you had this little inside alarm as if a little voice in your head.

In potions, you were listening carefully to what Professor Snape was saying, then you started thinking or daydreaming as you call it until the noise appeared. The quiet alarm inside your head. You lose focus. Looking around, you see Mattheo Riddle and his dark eyes staring at you.