Hi Melanie,
I completely agree with Heidi; you are dealing with old and embedded fears.
I'd suggest you figure out when the fear response begins. With one horse
that had similar saddling difficulties, I found that she would get tense each
time I entered her "space", beginning when I was about 10 feet away. I made
it a point to get this horse out several times each day, and to continuously
walk in and out of her space, always doing something pleasant once I reached
her (scratch a special spot, etc - anything which she normally accepted
calmly or with pleasure). While she was tied when I did this, she was not
cross-tied (that is, overly restrained).
Once she began to accept my proximity with less fear, I carried things with
me. She didn't react until I carried the saddle toward her, so I left the
saddle behind and carried the pad. I would put it onto her body as much as
she would let me, soon draping the pad over her, leaving it there, returning
and removing it, and repeating the process. I found it was easier at first
to drape the pad over her neck or over her rump than to place the pad on her
back as though I were about to saddle her.
Once she accepted the pad unflinchingly, I was able to add the saddle,
putting it on and going away, removing it, repeating the process. When I
added the girth, I was very careful to barely tighten it. With much
repetition and patience, this horse is now easy to saddle.
Of course, the obvious: be sure that your saddle fits and isn't causing pain.
Good luck!
Carmi