Well, in my case I believe that it was a normal reaction to an abnormal situation. After the birth of my first I had no energy or motivation, and would find myself getting irritated with the baby for just being a baby (in other words, for needing me.) I was really in a slump. Part of it was that I was not at all prepared for motherhood -- the pregnany has not been planned -- and I was having a hard time transitioning from being a hip and urban and social to being a SAHM in a small town, from being totally self-absorbed to having another being totally dependant on me. I also had a emotionally and physically traumatic birth, but because there were no complications and the baby was healthy, I felt like people would think I was a whiner, and I wasn't sure that I wasn't. I was also not comfortable in our living situation, and was in a transitional phase with my husband as well.
I believe that if I had had an empowered birth where I was treated with respect, if I was secure in my role as mother, in my relationships, and in my living situation, the openness that is birth would have been ecstasy. Instead, it made me even more vulnerable to all this negativity that already existed.
Anyway. I guess what I want to say is that while I don't believe it is normal to be so out of it after the birth of a baby, I think that it is sometimes a necessary defense mechanism, do you know what I mean? And I think that it is quite common in our society, so at least you are not alone. I encourage you to not be ashamed or guilty, and to not hide it, because that will slow your recovery. Good for you for seeking help!
The only other advice I have is to just take it one day -- one moment, really -- at a time. If you feel yourself starting to lose it, give yourself a time out. Meditate. Do yoga, get in touch with your body. Be kind to yourself, as in, don't sit there beating yourself up about your bad attitude. Pamper yourself as much as you can. Allow yourself to love you. Get help as much as you can. Surround yourself with people who lift you up, and avoid or ban people from your life that bring you down. It will get better.