Two things here from my perspective.

1) pinpointing exactly what it was / is that scares you. And challenging / managing that fear.
For me 'control' (or a lack thereof) was my issue. So I had to come up with ways to gain back my sense of control.

2) until you get (1) under control, don't try and visualize in such depth. Focus on breathing and relaxing all the muscles in you body and letting go if tension. If you are unable to skip over the fears and anxiety of birth itself, focus and visualize instead the happy outcome - you holding a nursing a newborn. Both of you content and happy.