Its hard I know. I am agoraphobic too...but for the past year I have forced myself to leave the house one day a week to see my therapist. Are you on any meds for anxiety? Will you have someone with you when you leave? That helps. I think once you get to the hospital and get settled in, chances are you will be ok. For me...its just the act of leaving the home that is the most tramatic for me.
Just remember. YOU WILL NOT DIE. You might feel like you will, but you wont. Breathe deeply, move quickly, and make sure the people at the hospital are aware of your condition.
Just like a band aid...it hurts less if you just rip it off.