I have had PTSD like responses to a recent past extremely stressful situation, and I found that  events that reminded me of that time triggered really intense physical reactions. I was completely not in control of these reactions. Racing heart, jumpy, dry mouth, shaky, dizzy, nauseous. You can't control those kinds of reactions. I'm so sorry you're having to deal with this.

Therapy will help you through this difficult time. your boyfriend needs to bear strongly in mind that now is not a good time to be deliberately startling you, though.