I think the most nerve-wracking, heart stopping moment for me was in Breaking Dawn when Edward found out that Bella was pregnant.
"A vampire who was still frozen on the floor with no signs of ever moving again."
Edward completely freaks and it completely freaked me out. I'm talking like physically ill for the whole entire Book II: Jacob until she actually has the baby.
Book II: Jacob - "They were all here, all together, but that was not what froze me where I stood and had my jaw dropping to the floor. It was Edward. It was the expression on his face. I'd seen him angry, and I'd seen him arrogant, and once I'd seen him in pain. But this - this was beyond agony. His eyes were half-crazed. He didn't look up to glare at me. He stared down at the couch beside him with an expression like someone had lit him on fire...."
"He raised his hand as if to wipe sweat from his forehead, but his fingers scraped against his face like they were going to rip his granite skin right off. His black eyes burned in their sockets, out of focus, or seeing things that weren't there. His mouth opened like he was going to scream, but nothing came out. This was the face a man would have if he were burning at the stake."
I will never, ever, ever forget this "burning man". Stephenie Meyer tortured my mind with this for a few good hours and it was excruciating. I was literally sick to my stomach and forced myself to keep reading until that half of the book was over.
The other part that had me upset was when Edward left, the last paragraph of Chapter 3 in New Moon. I have so totally felt like this before and it's amazing that my own feelings have been put into words.
"I felt the smooth wooden floor beneath my knees, and then the palms of my hands, and then it was pressed against the skin of my cheek. I hoped that I was fainting, but, to my disappointment, I didn't lose consciousness. The waves of pain that had only lapped at me before now reared high up and washed over my head, pulling me under. I did not resurface."
It reminds me of my favorite paragraph of Jane Eyre by Emily Bronte at the end of Chapter 26 -
"My eyes were covered and closed: eddying darkness seemed to swim round me, and reflection came in as black and confused a flow. Self-abandoned, relaxed, and effortless, I seemed to have laid me down in the dried-up bed of a great river; I heard a flood loosened in remote mountains, and felt the torrent come: to rise I had no will, to flee I had no strength. I lay faint, longing to be dead. One idea only still throbbed life-like within me - a remembrance of God: it begot an unuttered prayer: these words went wandering up and down in my rayless mind, as something that should be whispered, but no energy was found to express them - "Be not far from me, for trouble is near: there is none to help."............... "That bitter hour cannot be described; in truth, "the waters came into my soul; I sank in deep mire: I felt no standing: I came into deep waters; the floods overflowed me."