The reaction happened so quickly, Marie Davis barely had enough breath to call for help.

On Sept. 25, she saw a doctor to treat her bronchitis and sinus infection. The doctor wrote her a prescription for an antibiotic called Avelox and gave her a sample. Davis took the sample in her car, at about 9:05 a.m. Then she drove across town to Walgreens, dropped of her prescription and browsed the store as she waited for it be filled.

She figures about 15 minutes had passed since she took the sample dose to when she felt her throat close. She felt like she was underwater, drowning, unable to breath. She gulped in air, but remembers thinking it wasn't enough.

Alone in the store's aisle, she collapsed to her knees. She called as best she could for someone to call 911.

She remembers someone asking if she needed help. It was one of the last things she remembers.

"If it wasn't for our EMS system, I would have been dead," said Davis, who went into full respiratory arrest. She was taken to Wyoming Medical Center and spent four days in recovery.

She had taken Avelox before and remembers no signs of a reaction. No hives, no itching, nothing.

"The thing that people need to understand, just because you take something one time, doesn't mean you are safe. It's the subsequent times your body could react to," she said.

Davis had suffered anaphylactic shock, the most serve form of anaphylaxis -- a life-threatening, whole-body allergic reaction. It comes after the first time the body has been introduced to the trigger -- most commonly a food, medication or insect sting. The reaction is your body trying to defend itself, said Dr. James Bush, an internal medicine specialist and a staff physician with the Wyoming Department of Health. He is also the department's Medicaid and Medicare director.

"Your body decides, 'I don't like this. I need to fight it harder next time,'" Bush said.

So every time you are exposed to the trigger, you get a great immune response.

Between 1 and 2 percent people are at risk for an anaphylaxis, and between 500 to 1,000 people a year die from reactions in the United States.

Anaphylaxis is also under-diagnosed, Bush said. And he believes awareness and education are keys to avoiding these severe reactions.

Davis is a mother of two teenagers a year apart. She is also a nurse. If the reaction caught her off guard, she says, it could catch anyone by surprise. She hopes her story will bring awareness to others.

She will no longer take medications while she's alone, she said.

"If I hadn't gone to Walgreens, my son would have found me five hours later stiff and cold. Or, I could have killed someone," she said. "The first 15 to 30 minutes are so important. Everybody thinks about it with a shot, nobody thinks of it with a medication."

At the same time, the experience has impacted her professionally. As a nurse, she is more compassionate with the people she cares for and for her coworkers, she said.

"I think my family is very tired of the hugs and the kisses. It's brought my family much closer together.

"You just appreciate the fact that you are here. Even the arguing is music to my ears."

Anaphylaxis: what you should know

Anaphylaxis is a multi-system allergic reaction that is rapid in onset, said Dr. James Bush, an internal medicine specialist and a staff physician with the Wyoming Department of Health.

Anaphylactic shock is the most severe of these reactions and can lead to death in minutes if not treated.

"It is unpredictable. A lot of people might have a known allergy or have some previous mild reactions. Others might not be aware that they are allergic to anything. Even the first incident can be fatal," he said.

He believes anaphylaxis is under-diagnosed because the symptoms can often be attributed to other conditions or illness.

Triggers

While a long list of substances can trigger an allergic reaction, the three most common for anaphylaxis are foods, medications and insect stings.

* Food: For children, common food triggers are eggs, milk, peanuts or other nuts, fish, wheat and soy. For adults, it's most often peanuts or nuts and fish, especially shell fish.

"Shrimp and lobster are classics," Bush said.

"But we just say those are the common ones. It can be anything, and that's where it gets tricky. It can be fruits and vegetables."

* Medicines: Antibiotics, including penicillin, is the most common category. But common pain medications such as ibuprofen or aspirin can also trigger reactions.

"Any medication on the face of the earth can cause it, but these are statistically the most common," Bush said.

* Insect venom: Because these are injected into the body, reactions are usually very fast.

Symptoms

These will typically begin within minutes to an hour, though some people won't notice symptoms for several hours.

Less severe symptoms include itching, flushing, tearing and itchy eyes, sneezing, runny noes or nasal congestion. These can also mimic symptoms of a cold or the flu, so it can be hard to tell if they are the result of a reaction. Think hard about their onset and seek treatment if they come on suddenly after eating high-risk foods, taking medication or being stung by an insect.

Some of the more common and severe symptoms include:

* Hives: The swelling of the skin, either in bumps or inflammation, is the most common symptom of an allergic reaction. It occurs about 90 percent of the time. Angioedema -- a swelling of soft skin around the lips or eyes -- is similar and also a sign of a reaction.

Swelling around the throat can restrict breathing.

* Respiratory problems: These encompass anything related to getting oxygen to the body, including blurred vision, coughing, passing out and a drop in blood pressure. It is present in about half the cases of anaphylaxis, particularly in patients that have asthma.

A tightness in the chest, a swelling of the throat, dizziness or weakness are severe symptoms which need to be treated right away.

"In the most sever cases, you just suddenly collapse. That usually happens with a shot or an insect sting," Bush said.

* Other symptoms: Anxiousness, confusion or having a sense of doom. Swelling of the tongue, cramping or vomiting. With the last two, a reaction may be misinterpreted as food poisoning or the flu.

* Recurring symptoms: In up to 20 percent of cases, people will have a slight reaction and the symptoms will appear to resolve. But they will come back a few hours later, or in some cases, up to 72 hours later.

"So people will think, 'Whew! That's all behind me.' And the symptoms come back. It confuses people. And if they didn't see treatment the first time, they might have some serious problems," Bush said.

Risk factors

Anyone can have anaphylaxis reactions. But the follow three groups of people are more at risk of going into shock, or having a more severe reaction.

* Those with previous allergic reactions: If, in the past, you've had an allergic reaction to a trigger -- hives, shortness of breath, a little bit of an itch -- you are at a greater risk for anaphylaxis at a later date, Bush said.

"The severity of your reaction is not a predictor for the severity of the next."

* Those with asthma: If you have a history of asthma or other breathing troubles, you are at greater risk for a serious reaction. Asthma is already an immune mediated anaphylaxis disease in its own way, Bush said.

* Those with underlying health conditions: People with an underlying health condition may be less able to endure symptoms of anaphylaxis. If, for example, a person suffers from low blood pressure and a reaction causes his blood pressure to drop further, it could cause a heart a attack, Bush said.

What to do

So, what should people do with this information?

"Should we all walk around with doom and gloom?" Bush asked.

No. Be aware. Be smart. Pay attention to your body and its reaction to certain triggers, but use common sense, Bush said.

Here's what to do if you've had a reaction.

* Get treatment: Prompt treatment is key.

"If you've ever had anything like this before and you suddenly have symptoms, you need to get to an emergency room. Don't try to be heroic, because you can't hold your breath for very long," Bush said.

* Talk to your doctor: If you've had a reaction that required medical attention, follow up with your doctor. If the symptoms went away but you can't explain what caused them, also consider a follow-up appointment.

Taking a good medical history and physical is always a good first step. That will help you recognize symptoms such as shortness of breath or a drop in blood pressure, because you'll know what is normal for your body.

Pay attention to the medical screenings patients must fill out before every visit. Tell doctors about any reactions -- or suspected reactions -- you've had in the past.

* See an allergist: If you have had a reaction, even a minor one, consider seeing a specialist. Sometimes a trigger is obvious, other times it takes a little investigation. An allergist can help clarify triggers or might suggest other treatments.

* Carry medication: If you have a history of anaphylaxis -- or other reactions -- carry an epinephrine auto-injector. It injects a measured dose of medication to treat anaphylaxis.

Bush prescribes this to any patient who has had a reaction before. He also suggests wearing a bracelet identifying your allergies to alert medical personnel in cases where you cannot communicate the information yourself.

* Use common sense: Don't live your life in fear. While Bush believe awareness and education are always a good thing, these reactions are relatively rare.