Feeling anger is a normal human emotion, and the frequency and intensity of anger can vary from person to person. It's not necessarily bad that you don't get angry very easily and can work things out in your head. In fact, being able to manage and process emotions effectively is generally considered a positive trait.
However, the fact that you mention sometimes getting set off by little things and resorting to hitting yourself in the head to calm down is a cause for concern. Resorting to self-harm, such as hitting yourself, is not a healthy or effective way to cope with anger or any other emotions. It's essential to find healthier and safer coping mechanisms to manage emotions when they become overwhelming.
If you find that you're struggling to manage your emotions, particularly anger, consider seeking support from a mental health professional. They can help you explore the underlying reasons for these intense reactions and teach you more effective coping strategies.
Additionally, it's crucial to address any feelings of self-harm or self-destructive behavior with a mental health professional or a counselor who can provide guidance and support. Remember that you don't have to go through this alone, and seeking help is a sign of strength, not weakness.