I'm exactly the same as you, minus the CFS, and I was absolutely terrified starting my new job in October.I was literally being sick the whole week before and shaking constantly. There's not really anything I can do to make you feel better; just have it in your head everybody hates starting a new job, its a nerve wracking time. Just set yourself a timeframe in your head; see how you feel after a week, a month, 3 months. If you don't like it nobody can force you to stay, but obviously finding a new job is extremely difficult. Breathe, be polite and try to make friends.
Let me know how it goes