When a pet seems “a bit off” — quieter than usual, eating less, drinking more, hiding, or suddenly restless — the hard part is working out whether it’s a passing blip or the first edge of something serious. Animals often don’t show pain or illness in obvious ways, and by the time the signs are clear, the problem can be harder (and costlier) to treat.
Use the checks below to compare today’s behaviour with your pet’s normal baseline, spot the warning patterns early, and know when it’s time to ring your vet or head straight to an emergency clinic.
Start with your pet’s “normal”
Healthy pets are creatures of rhythm. They tend to eat, drink, move, sleep, groom, and toilet in fairly predictable ways. The most useful reference point isn’t another dog or cat — it’s your own animal on a good week.
Small changes matter most when they are:
- New (out of character for your pet),
- Persistent (not settling within a day), or
- Stacked (several changes at once: appetite, energy, toileting, posture).
Physical changes that often signal illness
Do a quick, calm scan once a day when you’re feeding or patting your pet. You’re looking for differences — not perfection.
Weight and body condition
Unexplained weight loss or gain is rarely “just age”. It can be linked to endocrine disease, chronic kidney disease, dental pain, parasites, or diet changes that aren’t suiting your pet.1, 2
Coat and skin
A coat that suddenly looks dull, greasy, scurfy, or is shedding more than usual can point to parasites, skin infection, allergies, hormonal disease, or nutrition problems. Persistent itch, redness, or hair loss deserves a vet check.
Eyes and face
Redness, discharge, cloudiness, squinting, or a newly “different” pupil can be a sign of pain or eye disease. Eye problems can worsen quickly, so don’t wait it out if it’s not improving within hours.
Breathing and gums
Noisy breathing, obvious effort to breathe, open-mouth breathing in a cat, or pale/blue-tinged gums are urgent signs. Seek veterinary help straight away.3
Behaviour changes that shouldn’t be brushed off
Behaviour is one of the earliest places illness shows up. Many animals will reduce activity, change posture, or withdraw when they’re unwell — it’s an instinctive pattern that can make subtle sickness easy to miss in a busy household.
Common behaviour shifts to note
- Lethargy (less interest in play, walks, or interaction)
- Hiding (especially in cats)
- Changes in sleep (restlessness at night, unusual daytime sleeping)
- Irritability (snapping, growling, avoiding touch)
- New clinginess (following you constantly, unsettled when alone)
Temporary stress vs illness
Pets can act differently after a move, a new baby, visitors, fireworks, boarding, or a change in routine. That said, stress doesn’t rule out illness. If the behaviour change lasts more than a day or two, or appears alongside vomiting, diarrhoea, fever, weight loss, or breathing changes, treat it as a health problem until proven otherwise.
Eating, drinking, toileting: the quiet early warning system
Appetite and thirst are simple signals that often change before anything else looks wrong.
Eating less (or refusing food)
Skipping a meal can happen. Ongoing appetite loss can be linked to dental disease, nausea, pain, infection, kidney disease, or many other conditions. If your pet is not eating and also seems quiet, vomits, has diarrhoea, or is losing weight, call your vet the same day.2
Drinking more and urinating more
Increased thirst and increased urination are classic early signs of several medical problems, including diabetes mellitus and chronic kidney disease.1, 2
A useful rule at home: if you’re refilling the water bowl more often than usual, cleaning larger clumps in the litter, or noticing bigger puddles in the yard, it’s worth a vet visit even if your pet otherwise seems “fine”.
Vomiting and diarrhoea
One vomit can be a minor upset. Repeated vomiting, vomiting with blood, or vomiting with diarrhoea can cause dehydration quickly and may signal poisoning, obstruction, pancreatitis, infection, or heat stress. Get veterinary advice promptly.3, 4
Diarrhoea that lasts more than 24 hours, contains blood, or looks black and tarry needs veterinary attention.3
When it’s an emergency
If you’re deciding whether to “wait and see”, use this: emergency signs are less about the diagnosis and more about the body failing to cope.
Go to an emergency vet now (or call ahead while you travel) if your pet has any of the following:
- Difficulty breathing, noisy breathing, or blue/white gums3, 4
- Collapse, severe weakness, seizures, or sudden inability to stand4, 5
- Repeated vomiting, especially with blood or with diarrhoea3, 4
- Swollen, hard, or rapidly enlarging abdomen (possible bloat in dogs)4
- Suspected poisoning or toxin exposure3
- Severe heat stress (frantic panting, drooling, weakness, collapse)5
Regular vet checks and prevention: why they still matter
Many chronic diseases are quiet early on. A routine examination can pick up weight changes, dental disease, heart murmurs, early arthritis, skin problems, or lab changes before they tip into a crisis.
As a baseline, most pets benefit from at least an annual veterinary examination, with more frequent checks for seniors and pets with ongoing conditions.6
Common preventative measures to keep on track
- Vaccinations: your vet will tailor timing to age, lifestyle, and local disease risks.
- Parasite control: flea, tick, and worm prevention reduces disease risk and discomfort.
- Dental care: dental pain is common and often missed until appetite or behaviour changes.
A practical way to monitor at home
If something feels off, write down what you’re seeing. A short log helps your vet spot patterns.
- Food eaten (normal / less / none)
- Water intake (normal / more / much more)
- Vomiting or diarrhoea (how often, any blood)
- Energy (normal / quieter / reluctant to move)
- Urination (more frequent, accidents, straining)
- Any new lumps, limping, coughing, or breathing changes
References
- Merck Veterinary Manual: Diabetes Mellitus in Dogs and Cats
- Merck Veterinary Manual: Renal Dysfunction (Chronic Kidney Disease) in Small Animals
- RSPCA Victoria: Issues Requiring Medical Help
- Animal Emergency Service: When to Go to the Emergency Vet
- RSPCA NSW: Heat Stress
- American Animal Hospital Association (AAHA): Frequency of Veterinary Visits
- Australian Government Department of Agriculture, Fisheries and Forestry: Protecting Australia from Rabies
- Australian Government DAFF: Rabies Vaccination and Tests for Cats and Dogs Coming to Australia
Veterinary Advisor, Veterinarian London Area, United Kingdom