It must have been awful and very, very traumatic. I can't imagine the pain and worry when your baby's every breath and fraction of an ounce had so much significance. On top of a traumatic birth.
I think you need to treat yourself very gently, you've been through the mill and it's going to have some effect on you.
I'm sure I've done that automatic cooing over newborns 'oooooh he/she is so adorable, so small and sweet!'
It's a general newborn thing like others have said and I will make an effort to change my automatic comments as I'd be so sorry to cause anyone pain when being awe struck at the wonder of life.
My DS was massive - suspected undiagnosed gestational diabetes and I was very sensitive about it. I didn't get to hold him for what felt like forever as they whisked him away as he was SO big they thought it might be a sign of something bad. Then he had problems with blood sugar and it was very scary - though not a patch on your experience I'm sure 
And then random doctors came up to visit him as the docs who did the csection had been gossiping about the mammoth baby in the staff canteen! I laughed and joked about him being a 'famous baby', but you know, underneath I felt terrible about it. Guilt, anxiety and then upset as a midwife said she couldn't see the fuss as he was just fat and large like his mother... Nice. I was fat because I was very poorly and couldn't move around, and was comfort eating, my natural size was 5ft 11 and size 8 so I already felt like I'd transformed into a walking blimp.
It's amazing how much people's words can embed into your brain/ heart at such significant moments in your life.
I think I had PND and wish I'd sought help for it. It's interesting to note that a pp said anxiety is a big symptom, that's important to bear in mind. A midwife told me (a different one from the fat comment one in hospital) that I couldnt have PND as I'd written a list of 30 questions to ask her, and detailed notes of every tiny thing he did as I was worried about so much after I got home. I'd say that was a clear sign of how anxious I felt, not a sign I was coping!
Anyway, I hope you get some distance between you and the traumatic stuff. And definitely try and be kind to yourself and don't be scared to tell people if you're feeling anxious or depressed as suffering in silence is rubbish! It can really eat into your early days with your baby and makes everything so miserable and hard.