Am I making it up in my head?

Yes and no, you are making it up in your head but also for some people it is caused by past traumatic experiences that you don't remember having

Depending on what it could be, but most of the time, regardless of whether or not you’re making it up, there’s always a meaning behind it, and that meaning can be the cause of a lot of issues involved in the area of negative mental health. For example, if you think you are overwhelmed by a number of emotions, and this could be strongly affecting your daily life, you could question as to whether you may have a mood or personality disorder. You could also question as to whether you’re making it up, however, regardless of this point, it’s always worth looking at why you could be feeling this way, just to be safe. It’s always good to tell someone about how you feel, and maybe eventually seek professional help. If you find that this still doesn’t help, it doesn’t hurt at all to ask a teacher, a friend, and tutor, a parent, a doctor, a coach, or anyone who is in a position of trust. If they fail to give you the help you need, they are failing their duties as a person of trust.