SYMPTOM
Behavioural changes
Owners may notice a dog becoming quieter and more withdrawn, irritable or less tolerant of handling, or restless and unable to settle, sometimes waking and pacing at night. Other changes include house soiling in a house-trained dog, new fear or aggression, getting lost in familiar places, and the loss of learned behaviours.
Neurological
Conditions affecting the brain, spinal cord, or peripheral nerves may alter awareness, responsiveness, or patterns of movement and rest. Changes in cognitive function, sensory processing, or motor control can each shift how an animal interacts with its environment.
Metabolic
Disturbances in organ function (liver, kidney, thyroid or adrenal) can influence energy levels, mood, and activity. Chronic shifts in glucose regulation, electrolyte balance, or hormone production often present first as subtle changes in demeanour or appetite.
Pain or discomfort
Musculoskeletal conditions, dental disease, or visceral pain may lead an animal to withdraw, become less tolerant of handling, or alter sleep and movement patterns. Pain is not always obvious and can manifest as irritability, restlessness, or reduced engagement.
Behavioural or psychological
Anxiety, fear, cognitive decline, or changes in social environment can each reshape an animal's behaviour. These patterns may arise independently or in response to shifts in routine, household dynamics, or sensory decline.
Infectious or inflammatory
Systemic infections, immune-mediated conditions, or inflammatory processes can reduce activity, alter appetite, and change social interactions. Fever, malaise, or generalised discomfort may shift an animal's usual patterns before more specific signs emerge.
Toxicity or exposure
Ingestion of certain substances, environmental toxins, or medication effects can produce acute or gradual changes in behaviour, ranging from lethargy to agitation. The timeframe and character of onset often reflect the nature and dose of the exposure.
Why timing matters
Early observation
When a gradual behavioural change is first observed, it may represent a transient response to a minor stressor, a subtle signal of an evolving condition, or the early stage of a more persistent pattern. The context in which the change appears (alongside other signs, after a recent event, or in isolation) can inform what it might reflect. At this stage, the picture is often incomplete. A sudden change alongside physical signs such as weakness, collapse, seizures or retching carries far more weight, because some of its causes can become life-threatening within hours.
Later presentation
If the change persists beyond a few days or recurs in a pattern, it tends to warrant closer attention. Sustained shifts in behaviour are more likely to reflect an underlying process than fleeting responses to environmental factors. The persistence itself can offer clues, as can any accompanying signs that emerge over time, such as weight change, altered appetite, or shifts in thirst or elimination.
Some behavioural changes remain stable, while others evolve by intensifying, improving or shifting in character. The trajectory can reflect the natural course of a condition, the effect of environmental adjustment, or the animal's own adaptation. Individual variation is considerable; what prompts concern in one animal may be less significant in another, depending on age, temperament, and baseline behaviour.
Conditions commonly associated
Pseudopregnancy (False Pregnancy)
False pregnancy can cause mood alterations including maternal behaviour, restlessness, reduced activity and aggression.
Acral Lick Dermatitis
Underlying anxiety or compulsive tendencies may manifest in other behaviours alongside the licking.
Brain Tumours
A tumour affecting the brain can alter mood, temperament or learned behaviours as it interferes with the areas that control them.
Glioma in Dogs
As a glioma expands within the forebrain, it can alter mood, temperament or previously learned behaviours.
Meningioma
Pressure on surrounding brain tissue as this slow-growing tumour enlarges can gradually alter temperament, alertness or normal routines.
Pituitary Macroadenoma
Mass effect on the brain from this tumour can alter normal behaviour, from withdrawal to uncharacteristic irritability.
Aggression in Dogs
Aggression can emerge as part of a broader shift in temperament and behaviour, rather than appearing in isolation.
Ovarian Remnant Syndrome
Residual ovarian tissue continues to produce hormones after spaying, and the resulting hormone surges can bring back heat-associated changes such as restlessness, increased activity, vocalisation or urine marking, with or without attracting male dogs.
Pain-Related Aggression in Dogs
Underlying pain often shows itself first as a shift in temperament, with irritability or defensiveness appearing where none was present before.
Gastric Dilatation-Volvulus (GDV) in Dogs
Restlessness, drooling and repeated unproductive retching with a swelling belly can be the first change owners see, and the condition can become life-threatening within hours.
Xylitol Toxicity in Dogs
Low blood sugar after eating xylitol can cause sudden vomiting, weakness, wobbliness, lethargy or seizures.
Canine Cognitive Dysfunction
In older dogs, disorientation, disturbed sleep with night-time restlessness, house soiling, changed social interactions and anxiety can reflect age-related cognitive decline.
Hypothyroidism in Dogs
An underactive thyroid can bring lethargy, reduced responsiveness to surroundings and sometimes irritability.
When to explore further
If the change is marked, persists beyond a few days, or represents a clear departure from the animal's usual character.
If it occurs alongside other observations, such as altered appetite, weight change, increased thirst, vomiting, changes in gait, or shifts in elimination patterns.
If the animal becomes less responsive to familiar cues, appears disoriented, or shows reduced awareness of its surroundings.
If the behaviour interferes with daily routines, such as eating, resting, or interacting with the household, or if it causes distress to the animal.
If the change came on suddenly, over minutes to hours, or followed possible access to substances, plants or medications. Xylitol, a sweetener in some sugar-free products, can cause vomiting, weakness, wobbliness, lethargy or seizures from low blood sugar within 30 minutes of being eaten, or after a delay of up to 12 to 18 hours. Restlessness with drooling, repeated unproductive retching and a swelling belly can reflect gastric dilatation-volvulus, where signs lasting more than six hours before a vet examines the dog are linked with a higher risk of death. Blood sugar and a twisted stomach cannot be judged at home.
Behavioural changes gain meaning when considered alongside the full picture: other signs, the timeline, the animal's history, and its usual temperament. Keeping a brief note of what has been observed, when it began, and how it has shifted can be useful context. These observations, paired with a conversation that takes into account the individual animal, help build a clearer understanding of what may be unfolding.
Last reviewed: 9 October 2026 · Dr Alastair Greenway MRCVS