Smells, motion and noise are often triggers. Sometimes it's just the barometric pressure and humidity.
For Erick's former patient, Jacinta Telesford-Ximba, who threw up 8 to 20 times a day before having twins at 36 weeks, it was motion and food.
"I couldn't drive in a car," said the 38-year-old nurse from West Roxbury, Mass., who sought help from Erick.
"No one could cook in the house at all," she said. "I couldn't have anyone eat in front of me. The way people would eat or the way it was presented on a plate. I couldn't see salad bars or big entrees or even go to the [hospital] cafeteria."
She could barely look after her 3-year-old son and was confined to bed for months.
"The day I delivered I was still throwing up," she said. "I was in the hospital so often with an IV tube my veins were gone. That's how sick I was. And there is nothing you can do."
"There were days I thought my god I am dying," she said. "It's like circling down a drain."
Many of these women end up in the hospital dehydrated, with "mild starvation" and electrolytes out of balance, according to Dr. Dwight Rouse, an obstetrician from Women and Children's Hospital in Providence, Rhode Island, who works with high risk cases.
Severe dehydration can result in heart irregularities and even heart failure.
Rouse has seen patients with life-threatening electrolyte balances who vomited "to the point where they threatened their own health" and aborted.
Just last week, the British press reported that Cheryl Harrison, threw up 40 times a day and couldn't take care of her 5-year-old. She made the agonizing decision to abort at nine weeks.
She admits the termination was the "most horrendous decision I have ever made."
"I think there are other women who have terminated pregnancies for the same reason but it's a taboo, no one discusses it," she told the Daily Mail newspaper.
Karen Williams of Elmira, Calif., was hospitalized with hyperemesis 30 years ago while pregnant with her daughter. She was so malnourished her hair, eyebrows and eye lashes fell out and her nails split.
"I almost thought of not having her because I had never heard of anyone as sick as I was," Elmira wrote to ABCNews.com. "I was so sick and it was the most horrible nine months of my life. Whoever said you glow when pregnant had never met me."
In the United States, about 59,000 women are hospitalized with the condition each year, according to Marlena Schoenberg Fejzo, a UCLA researcher and geneticist, who is leading a study to find genetic causes for hyperemesis.
Until now, doctors have suspected that the pregnancy hormones - estrogen, progesterone and human chorionic gonadotrophin (hCG) -- were to blame for morning sickness.
Some studies have implicated the olfactory system, which is responsible for taste and smell and even the H-pilori bacteria that causes stomach ulcers. Some studies have even looked at thyroid gene mutations and stomach rhythms to try to understand what sets off the brain's vomiting center.
But newer research, showing that women with mothers and sisters with the disorder are at greater risk, suggests that there may be a genetic component.
"Hopefully it will lead to better treatments," said Fejzo of the UCLA study. "The limiting factors are getting enough participants -- 1,000 cases and 1,000 controls -- and getting funding for the genetic analysis."