POTS? Or something else?

Hello, I 19 y/o F, have had a pacemaker since birth. So it’s always been a part of my life. I have complete congenital heart block on the lower quadrants and haven’t really had any problems in life with this. However, I noticed about 2-3 years ago that I’ve been getting really awful heart palpitations, becoming very very out of breath, shaky, lightheaded, and sometimes my face will become tingly and numb for a while. It makes me incredibly tired and fatigued. Sometimes a little nauseated. My cardiologist said it could be anxiety and kind of brushed it off about a year or so ago but nevertheless, it’s persistent. I told her at my last appointment that it’s still happening, almost as if I need to pass out but can’t. Her exact words were “You cannot pass out since you have a pacemaker. You’re probably feeling that way and staying conscious because your pacemaker will not let you pass out.” Yesterday, as I was out and about, I had to sit in the floor of a bookstore because I felt extremely lightheaded, terrible heart palpitations and my face felt numb. Today, it’s happened about 3 times off and on. I’m currently sitting in my bed because of it. My mom and I have noticed I have every symptom of POTS but I’m curious if it could be something else. I have a doctor’s appointment soon and I am going to tell my doctor everything about this in hopes to get a referral somewhere. Does anyone know maybe what else this could be, or have experienced anything like this? My pacemaker battery life is also pretty good, so that wouldn’t be at fault.