I'm going to play Devil's Advocate here, so bear with me before slapping me.
Janet, what you described happens sometimes. At least it's happened to me. Most of the time you get an immediate release that you can feel.
But sometimes, yes, it can feel worst at first. There's usually two reasons for this. One is if you're tensing up while they're trying to do a manipulation, you make their work harder and yep, it causes pain.
The second reason is: If you've "caught" one of your vertebra on another and it's causing you pain, and then she "un-catches" it,....think of it like this: If you hit your thumb with a hammer, obviously your thumb is in pain. But for it to heal, the hammer has to be removed. When you remove the hammer, it still hurts, right? And sometimes it throbs or hurts a little more, but the source of the pressure is gone.
By all means if you're scared or unhappy, it's your body, protect it, don't go.
I went for so many years as did my whole family because we had excellent results. We also learned how to relax (which as you pointed out, is quite key).
These "catches" generally go away......eventually.
And finally, like anything else, maybe it was the practitioner? Like any other field, you're going to find the good, the bad, and the mediocre.
M.