Janette Sherman, 38, a recent transplant to Colorado, recalls how a casual walk with her dog last month turned into a frantic trip to the ER—and the mistakes she made along the way.

On one of the first warm days of April here in Denver, I set off on my lunch break for a hike in nearby Bear Creek Lake Park. I work for a cycling company where most people ride for an hour in the afternoons, but I had my dog with me that day and he needed a good walk.

I moved to Colorado last year from California, and my boss had warned me about rattlesnakes on the trail—especially in the spring, when the ground starts to warm up and the cold-blooded critters look for places to soak up some sun. Still, I’ve encountered snakes before and wasn’t overly concerned: I was wearing shorts (instead of pants and snake gaiters, like some experts recommend), and certainly wasn’t watching the ground every step of the way.

Almost a mile into my hike, I felt a sharp, sudden pain on my ankle, like I’d been stung by a wasp. I looked up, expecting to see a bug flying away. Then I looked down and saw the obvious puncture wounds.

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I glanced behind me and saw the snake, coiled up, ready to strike again. It wasn’t particularly large—its coil was maybe 6 inches across—and it hadn’t rattled, the warning sign that often alerts people to back away. I wasn’t sure what kind of a snake it was, but I knew I should call 911 just to be safe.

The dispatcher asked me if my bite looked like a horseshoe; I learned later that horseshoe-shaped wounds come from nonvenomous snakes with tiny teeth all the way around their mouths. When I told her no, there were three distinct holes (which indicates the fangs of a venomous snake), she calmly told me I should get to a hospital.

But at that point I still felt OK, and was embarrassed to make a big deal about things. Even though the dispatcher wanted to send an ambulance, I told her I’d walk back to my car—the long way, since I refused to backtrack past where the snake had been—and drive myself to a fire station down the road.

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As I walked, my foot began to swell and hurt badly. A driver on the road saw me limping and gave me a ride to my car, and I managed to get myself to the fire station. I was sweating a lot more than normal, and my lips and face had started to go numb. Now I know that overexertion can speed up a person’s reaction to snake venom and make symptoms worse. Looking back, I should have waited for help to arrive.

At the fire station, the EMTs took my shoe off and used a Sharpie to mark how far the swelling had spread—up my leg and across my foot—in the 30 minutes since my bite. This would help the doctors determine how serious my case was, they explained. (They also told me that commercial “snake bite” kits are worthless, but that hiking with a permanent marker is a good idea for this very reason.)

I asked if I could go to an urgent care center, but the EMTs told me that only major hospitals would have antivenin, the technical name for what's also known as anti-venom. About two out of five rattlesnake bites are what’s known as a “dry bite”—not venomous—but with my swelling and facial numbness, that didn’t seem to be the case.

An ambulance took me to Saint Anthony’s Hospital in Denver, where the paramedics' suspicions were confirmed. But the antivenin had to be mixed in the pharmacy—it’s not always stored in a ready-to-use formula—which would take a while. I was seriously starting to regret not agreeing to an ambulance right away.

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In the meantime, the doctors performed an EKG to check my heart rhythm, and gave me anti-nausea medication to keep me from throwing up (a common symptom of snake bites). Then, about two hours from when I was bitten, I started seeing double and my vision began fading to black. In the nick of time, the antivenin was ready, and the doctors administered six vials.

Over the next few hours, I received six more vials as the hospital staff monitored my vital signs, making sure I didn’t have a bad reaction to the drug. Snake venom can interfere with blood cells’ ability to clot, so my doctors also had to take frequent blood draws and pay close attention to that, as well.

The pain from the swelling in my leg was excruciating, and I had to be monitored closely to make sure I didn’t develop compartment syndrome, when pressure builds up and causes tissue and blood vessel damage. But I got really lucky: Because I’d been treated quickly enough, I didn’t have any permanent injury.

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I spent about three days in the hospital, and was discharged with crutches and some strong pain meds. I was cleared for exercise, and went back to the office, a week after the bite happened. I’d tried to answer work emails while recovering at home, but I felt really out of it those first few days—like my brain wasn’t working at full speed.

Then came several follow-up appointments, with an orthopedist and my primary care doctor, to make sure there were no lasting complications. My liver enzymes tested a little high, so I was told not to drink alcohol or take acetaminophen for a month.

It’s now been about three weeks since I was bitten, and I still have tenderness and swelling in my leg—especially if I spend a lot of time on my feet. But the bruising has faded and you can barely see the puncture marks. Also thankfully, I have health insurance: I haven’t gotten a bill yet, but I’ve read that antivenin can cost $2,500 a vial, and that it’s not unusual for snake-bite treatment to total $100,000 or more.

The most lasting effect of all this, honestly, is that it’s made me a little freaked out to go back out on the trail. I finally went for a bike ride at Bear Creek Lake this past weekend, and I screamed a few times when things brushed my leg. Luckily, I was able to calm myself down with some deep breaths and logical thinking.

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I did learn a lot from my experience— that rattlesnakes don’t always rattle, how to recognize a venomous bite, how important it is to get to a hospital ASAP, and what not to do: Experts agree that you shouldn’t apply ice, cut into the wound, raise the affected limb above your heart, or apply a tourniquet.

I do plan to buy some snake gaiters, especially for when I’m exploring on foot, and I’m sure I will be more cautious from now on when I do get back out there. I know I’ll get my confidence back soon, though, because hiking and biking is what keeps me happy and healthy—rattlesnakes and all.

As told to Amanda MacMillan