Dacourse I found out on Tuesday afternoon that I'm 8 weeks pregnant with fraternal twins (same as you?) and I'm feeling EXACTLY the same thing!
We went in, because my symptoms over the weekend were very different from my first pregnancy (DD nearly 4) - lots of pain and lightheadedness, light bleeding...I really was expecting the worst. The news we received was pretty much the exact opposite of what I was expecting to hear! Once I saw the two foetal sacs I had my hands over my face for the rest of the scan in shock!! 
I am so worried about how we will cope, but we'll just have to. And I'm worried about how tired I'm already feeling compared with last time. I can see CBeebies time for my DD extending everyday until she has square eyes if I'm not careful!
We've recently moved to a new part of the country, so don't have any friends or family locally for support, though I know our loved ones will do all they can when they can. I've already decided to be as proactive as I can be (given all I want to do is sleep right now) and find a TAMBA group or NCT twins group to meet other people who have gone through or are going through the same thing. And I liked kickedinthetits point about lowering expectations...I'm planning on putting pride to one side for the next 18 years.
I have an older sister who has four grown-up children, she had identical twins when her two older ones were 4 and 2. Out of everyone in my family she is the calmest, most laid back and gentle personality. I don't remember her always being like this: it came as a result of just having to change gear as a mum of so many little ones. Her children all have a great bond and the older ones have always had the twins under their wings. Among the shock, I am finding their family dynamic quite comforting.
Do you want to know the most ridiculous thing? I'm one of those control freak women, who always had a plan for the age gaps between her children. My DH and I agreed on two basic things when it came to our family: no double buggies and no two members of the family in nappies at the same time. HA!! Best laid plans hey?