Making up fictional stories in your head is a common and normal human experience, and it does not necessarily mean you have a mental illness. Many people have active imaginations and engage in daydreaming or creating elaborate stories in their minds.
However, if these fictional stories are causing distress, interfering with your daily life, or becoming difficult to differentiate from reality, it might be worth considering talking to a mental health professional. They can provide a proper evaluation and help determine if there are any underlying issues that need attention.
Remember, seeking help from a qualified mental health professional is always a good idea if you have concerns about your mental well-being. They can provide guidance and support tailored to your specific needs.