My DH says that finding out your wife is expecting is very scary, even when you've been TTC for ages. You suddenly feel very left out - everyone is interested in your wife (not you), how she feels, what's happening to her etc. People talk to your wife about how excited they are for her, but not to you. Plus she can imagine what life with a baby might be like, which men often find harder, having talked to fewer people about it, and having read fewer books/websites etc. For the dad, it feels much more like a scary unknown and the only things you can feel confident are that you will be chronically sleep deprived and lead a miserable life for the first little while after the baby arrives.
My DH has been really good, but I can see how some men completely freak out. I think you need to try to show him sympathy and understanding, tell him how you feel, and try to involve him in the baby things as much as possible.
One of my husband's colleagues told him that he now always feels he comes last in the family pecking order, after the children, and that he is now the least important person in the family. I think a lot of men start to worry that this will happen to them once their wife gets pregnant, so it's really important to make sure you show that you still love and care for your DH rather than emotionally 'deserting' him for the baby. I'm not at all suggesting that's what you're doing, but I think that's how many chaps feel, and it can make them go a bit bonkers trying to cope with it all.
I really hope things improve for you. I'm sure that as he gets used to the idea, he'll calm down a bit.