Dentist anxiety..what should I do?

When I was a child going to the dentist scared me to death then as I got older I was ok with it but this past year or two ago the anxiety has gotten ten times worse. Just think about going to the dentist makes me incredibly nauseous and dizzy, so when I’m at the dentist I of course feel like that. Nausea and shoving things in your mouth don’t go well together. I have a sensitive gag reflex and a tiny mouth so that also adds to the anxiety. I also have POTs and migraines so laying all the way back in that chair triggers my heart rate and vertigo issues. I’m not sure what I should do and why it’s gotten so much worse. My last dentist appointment in May I left half way through the cleaning because I felt so sick.