The most important thing to learn from my experience will be the first and the last thing I say in it: if your pet has a sudden change in behavior, get help immediately. Don’t walk—run to the nearest vet and figure out what’s going on.

It all started in March. For the two years that I had been living with my fiancée and her adorable, feisty furball India, I was greeted at the bed by a head-butt and a purr every evening when I got home from work. Head-butts and purrs usually lead to a happy kitty having attention lavished upon her. So when I came into the room for a week straight without being greeted, I was worried. What was even more concerning was the fact that she was sleeping alone under the desk, rather than nestled between our legs like usual. Well, everyone has an off-week, right? Besides, it was a particularly warm week; I figured that India just didn’t want to heat herself up any more than absolutely necessary. But when I got the chance to break out the laser pointer, then the catnip mouse, and then a long colorful shoelace with no response, some small voice of panic inside of me welled up and shouted that something was wrong.

A quick Google search told us that severe lethargy in cats can be capital-B Bad. Or it could mean nothing. But when it comes to the lives of pets (a.k.a., family), always err on the side of caution.

It was already after-hours at the vet when we were incited to action on Friday night, and our normal vet was out of the office for the next week on vacation. So, we found the next closest vet with the next closest appointment—I worked from home Monday so that I could bring India in as soon as the clinic was open. (My boss and coworkers were extremely understanding throughout this process, allowing me to work remotely. In any case, it wouldn’t have stopped me from getting India the attention she needed.) Into the carrier and off to the vet we went!

When your cat is healthy, you don’t necessarily pay attention to things like their urination or defecation. This is especially the case if you have a closed litter box and clean it on a regular schedule instead of checking daily. But these are things that the vet wanted to know, and they were answers that I couldn’t readily produce. As an indoor cat, we thought that the vectors through which India could be hurt were minimal. They told me to keep an eye on her and bring her into our normal vet as soon as possible since blood tests and x-rays showed no problems.

Rallied by the “all clear” that I received from the first vet, we thought that maybe India was just feeling a bit older and didn’t feel like moving around as much in the heat. Regardless, we got an appointment with our vet and brought her in together. Once again, blood tests and urine tests were performed, and everything came out as “normal.” Our vet asked us about a few common household chemicals and whether or not India had been around them. Of course, she hadn’t. The vet thought that maybe she had gotten into something and just needed her system flushed, so we left her at the clinic overnight to get some extra observation and IV fluids, and were hoping to pick her up the next day.

After observing her overnight, the vet decided that they wanted to keep her an additional night. On the phone, the vet asked us once again if there was anything that she could have gotten into. “We don’t even have human food where she can get to it. The only things that she can easily get to are her food and water. She gets a catnip toy when supervised, and we give her flea medicine to her every month…” The vet took some notes and said that she would get back to us the next day. We picked her up two days after dropping her off, and the vet gave us the likely culprit: her flea medicine.

Our vet had gone through the flea medicine’s ingredient list and had done research on each item. The “organic” and “green” flea medicine that we were using (stocked at a small child’s eye-level at Safeway and Petco) contained an ingredient that was so toxic that humans were required to wear skin- and eye-protection when handling it. This wasn’t the typical “IRRITANT” label that anyone who has used sunscreen is used to. As for the products claims of being “green,” our vet helpfully pointed out that arsenic and cyanide are “natural and organic” as well. If the medicine’s ingredients can cause such severe harm in humans, how much worse is that damage for a being that’s a tenth of our size? Quite a lot worse, as it turns out.

Had we had any previous indications or reactions, we may have looked online and seen the hundreds of reviews of this particular product, many claiming that their pets were poisoned almost to the point of death (or were sadly killed) by this product. Since this happened as a result of the build-up of over a year’s worth of applications, we never suspected that something that hadn’t caused her any issues before was the culprit of her sudden health problems. How were we supposed to know that counterfeit and bogus flea medicines are some of the pet industry’s top money makers? The vet informed us—our mouths agape—that some popular flea medicine brands are counterfeited so convincingly that grocery suppliers often can’t even tell the difference, leading them to be stocked at your friendly neighborhood corner store.

For a week after we got her back, we had to give her daily subcutaneous fluids to help flush out as much of the poison as possible—this meant we had a giant bag of saline hanging from our ceiling fan, and every day started and ended with one of us holding her down while the other shoved a needle of cold fluid into her neck. We’re now almost three months after the fact, and India still hasn’t recovered. Because of her lethargic response to the poisoning, not moving around caused severe muscle atrophy in her hind legs and she now has a hard time getting around and doing normal kitty things—holding herself up in the litter box, jumping on anything, walking across the room. We have done everything we can to make sure that she’s comfortable and happy, including replacing her litter box with one that has a lower wall so that she can get into it easier and adding a set of kitty stairs to our room so that she can get off the bed easier. We’ve taken her to a feline physical therapist, and now have a set of rehabilitation exercises that we perform with her morning and night.

Even though we’re still working through the mechanics of this ending (and it isn’t exactly the happiest), we now have a story to share with all pet owners: only trust the flea medicine you get from your veterinarian, and if your pet has a sudden change in behavior, get help immediately.