Hey Josie!
I have a fear of that faint feeling also. I get it all the time! I know I make it worse by thinking about it, but it's so hard to ignore when you feel like falling over any minute. I get it mostly in the mornings and while at work. I also get it when I'm out somewhere like the store or standing in line somewhere. I just keep telling myself that it is a normal physical reaction to anxiety and even though you may feel like passing out, it's not likely. I asked a doctor about this once and she said that unless you have a history of passing out, it's very unlikely that you will. I have to keep reminding myself of that over and over when I'm panicking about it. I seriously hate that feeling!!
You say that you tense up a lot and shake. That is why you are having back spasms. We carry the majority of tension in our neck, shoulders and back. I also have a problem with muscle tension in my back that affects my left arm. I have learned the only thing that really helps this is stretching. When you start feeling tense in your muscles, stretch, stretch, stretch.
When you go on your trip, keep reminding yourself that you will be ok. I know it doesn't feel like it at the time, but you have been through this so many times before, you will make it through it again. Panic will not hurt you. The physical reactions will not hurt you. It may feel like it, but remember that you will be ok and you will make it through the attack. Positive self talk and deep breathing is the key. Just keep telling yourself over and over, you will get through this and everything really is ok.
Hang in there and let us know how your trip goes! I promise you will be ok!!