Every pet, throughout the course of their lives, will encounter some health issues. Even with annual vet checkups (and these are a must), your pet will occasionally show signs that all is not quite right in their world. Unfortunately, pets can’t tell us what’s wrong, so it’s easy to overreact—or worse, underreact—to any given situation.

“Pets want to please their owners and are great at hiding pain or discomfort or if they are simply not feeling well,” says Dr. Mel Paquin, chief medical director of the Animal Medical Center of Surprise in Arizona. “[They] will have a much better prognosis if you are proactive in getting them seen by a professional.”

Of course, this doesn’t mean you have to drag your dog to the vet every time his dinner doesn’t agree with him. But there are some conditions that should set off alarm bells, as they can indicate something seriously wrong. We’ve compiled a list of these conditions that cannot wait. If you see these signs, you’ll need to take your pet to the vet immediately.

1. Difficulty Breathing

“If a dog or a cat has an increased breathing rate or an increased respiratory effort, they should be brought to a veterinarian immediately,” advises Dr. Virginie Wurlod, assistant professor in small animal and emergency critical care at the Louisiana State University School of Veterinary Medicine. Difficulty breathing can indicate a host of life-threatening conditions, Wurlod says, such as pneumonia, congestive heart failure, heartworm, severe anemia, or disease of the pleural space (between the lungs and chest wall). A veterinarian will need to monitor your pet closely, perform a physical exam, and run tests to determine the cause of the breathing difficulties, and treatment varies based on diagnosis.

2. Severe Vomiting or Diarrhea

Vomiting and diarrhea are an occasional fact of life with pets. In dogs, in particular, diarrhea and vomiting are common consequences of a change in diet, eating too much or too fast, or eating that spoiled Taco Bell burrito they found in the park. But frequent and severe episodes of vomiting and diarrhea in pets can indicate serious medical issues, especially when accompanied by symptoms like lethargy (“If your pet is lying around, doesn’t greet you at the door, or is hiding,” according to Paquin), pain, or pale gums. “Diarrhea and vomiting can be caused by dysfunction of many different organ systems, like the gastrointestinal tract, pancreas, urogenital system, or liver,” Wurlod says, adding that leaving these conditions untreated “can also lead to severe dehydration.” A veterinarian can prevent or treat dehydration by replenishing your pet’s fluids, while also running tests to check for underlying medical issues.

3. Inability to Urinate or Severe Constipation

While diarrhea is a bit more obvious, you also need to be aware if your dog or cat is suddenly not defecating or urinating. “If you are not seeing urination within a four- to eight-hour timespan, this is a sign that the pet should be taken to a doctor,” Paquin states (though the timeframe may vary by pet, how much they drink, and how often they typically urinate). And if a pet makes frequent attempts to urinate without being able to do so, something is up. Likewise, with defecation, you should be aware of any deviation from your pet’s normal habits. Paquin notes that “vocalization upon urinating or defecating” should be particularly alarming, as it means your pet is likely in pain. This can suggest “a complete blockage of the urethra,” he says, or colon in the case of constipation. These symptoms can stem from infections, tumors, physiologic or metabolic disorders, lesions of the spinal cord, and more.

4. Active Bleeding

Sure, dogs and cats cut themselves every now and then, just like we do. But as with vomiting and diarrhea, degree of severity is important to note here. If a pet is bleeding profusely, the American Veterinary Medical Association recommends covering the wound with a gauze pad and applying pressure to it. Check after a minimum of three minutes. If your pet continues to bleed after several minutes, emergency care is the best recourse. “Any active bleeding should always be investigated,” Wurlod advises. “It can be a result of a traumatic injury and require surgical treatment, or could indicate an abnormal clotting ability or other systemic disease.” If your pet’s blood is not clotting properly, expect your veterinarian to run a number of tests before implementing a course of treatment.

5. Distended Abdomen

If your dog or cat has a noticeably distended abdomen, it’s extremely important to get it checked right away, Wurlod advises. “It could be associated with a food bloat, but could also be seen in a patient with a large amount of abdominal effusion [free fluid] or gastric dilation and volvulus (GDV),” she says. It’s especially important for large dog owners to be observant of these signs, as GDV is most common in large breeds. “Dogs presenting with GDV can be restless, in pain, retching but unable to vomit,” she adds. According to the American College of Veterinary Surgeons, treatment for GDV includes intravenous fluids, oxygen therapy, gastric decompression, and surgery. “If left untreated, these dogs’ cardiovascular function will be affected” and they often die, Wurlod warns.