She describes her state of mind that day as "hell, hell inside of my mind. That's all I can say and I couldn't stop myself."
She tells 48 Hours Correspondent Susan Spencer that voices in her head were convincing her that Nathaniel was cursed, that he would die if she didn't get him to a Catholic church.
"I couldn't stop running from trying to get him somewhere that I thought was going to save his life, break this curse," Branson says.
"I heard and felt that I was supposed to let go of the wheel of the car. Let go of the wheel and the gas. And then I was just, like. 'I can't do that. I can't.' It's, like, 'Don't you trust God?'"
Did Branson let go? "I must have," she says.
The result was a head-on collision in which Branson lost her only child.
"I know what it is like now to have been insane," she says.
Branson had no idea at the time, but she believes today her psychosis was a reaction to the drug Adderall, which had been prescribed for her attention deficit disorder.
"That person that was in that car that day was not Dawn Marie," says her father, Tony Frushon. "The bottom line is, if she wasn't on this medication, this wouldn't have happened."
Branson had previously been hospitalized for depression but had no history of psychosis. She had started taking Adderall three months earlier, when her doctor suggested the drug might help her concentration. She said he didn't tell her about any possible side effects.
Recently divorced, Branson had planned to go back to graduate school. Because she had struggled in college, she wanted to make sure this time she'd be able to focus.
"If I heard someone next to me rustling paper or kind of tapping the pencil," she says, "that's what I'd be focusing on."
At first, she says, Adderall did wonders, helping her to concentrate and focus. But two and a half months later, she began to turn on her family, and she started hearing voices.
"We thought she was having a nervous breakdown," recalls her mother, Marge Frushon.
Tony adds, "The night before the accident, we could see that the baby was even disturbed, uncomfortable. And this is when we looked at each other and said, 'Something is wrong with Dawn Marie.'"
They had no idea what that something might be. Branson had never told them she was taking Adderall.
"I said, 'Dawn, please do it for dad tomorrow. I want you to go to a doctor. I'll go with you' and she says OK," Tony says.
But the next day, Branson got up early, grabbed Nathaniel and took that fateful drive.
"I never got a chance to hear him say 'I love you. I love you, mom,' " Branson says. "I miss my baby. I miss Nathaniel more than words could ever say."
What happened to Dawn Branson is tragic, but to the millions of Americans who take Adderall with no side effects, her experience also seems unimaginable. In fact, many of them call Adderall a miracle cure for attention deficit disorders.
"It was the single most extraordinary experience of my life," says Eileen Lagrotta of the drug that changed her life. She describes ADHD as having 10 radios playing in your head all at once, but says she noticed a difference within a half an hour of taking her first dose of Adderall.
"All those radios were quiet for the first time," says Lagrotta, who lives in St. Louis. "It gave me an opportunity to turn my life around, really. It's phenomenal. I mean, just to have my head so noisy and so cluttered with negativity for 40-something years and then to have it quiet."
Adderall not only turned around her own life, Lagrotta says, but also the lives of her two children, Matt and Tony. It was through her children's diagnoses that Lagrotta came to realize she, too, had ADHD.
"If I didn't have my pills, I couldn't sort these," Matt says, pointing to a pile of baseball cards. "I would have to jump up and do something else. I just couldn't do it, but the pills made a big difference for me and I think it made a good change in my life."
But Dawn Branson is convinced that Adderall cost her her only child. She is angry at the makers of Adderall, Shire Pharmaceuticals, for not adequately warning her that psychosis is a possible side effect. The company, she says, "had the responsibility to inform me through my doctor that this drug is capable of doing this."
How did the company respond to this charge? Find out, in Part 2.