@Seline , I completely agree that you need validation. I agree with @Quartz2208 , but I also think (with the greatest of respect) that you are angry with the only person you can be angry with.
Your birth was traumatic. Those people were 'justifiable' in their handling and treatment of your body, for medical reasons, as their actions had a purpose: to keep the three of you alive. Logically, you cannot be angry at them because you are all still alive and thriving.
And so you are focusing your anger on your MIL because you cannot understand her actions.
As I see it, it's quite simple. You are heading down for theatre, when 26 weeks pregnant, with twins. It's an emergency. And in emergencies, the most carefully laid plans can go out the window because all we usually want to do is make sure our loved ones are safe. It's instinct. I would drop everything for most of my family and friends under those circumstances, and peg it there, let alone my son. People would have to hold me back. She was probably out of her mind with worry, and needed to be there, to offer support, to be on hand, to be close.
I am in no way saying that her needs trumps yours, but what I am saying is that I can understand her. It is unfortunate that you opened your eyes at the moment she was stood over you, but she probably wouldn't have been in that position for very long.
I also think that she will not apologize but I do not think YABU in wanting your feelings to be validated.
I am very very very sorry that you have gone through what you have, I really am. I don't know you, and I am not offering any diagnosis but what you are writing does indicate that perhaps talking through your feelings with a professional would help. 

