The jump down from a car boot looks routine because dogs do it every week, but the landing loads the neck, shoulders, and spine all at once — and a dog who jarred something on that landing rarely shows it with a limp. He shows it by quietly reorganising his day around movements that now hurt.
The movements he starts avoiding
Compare today with his normal habits. A sore-necked dog often hesitates at the bottom of stairs he usually takes freely, pauses before stepping up a kerb or onto his bed, and lowers himself down slowly instead of flopping. He may stop shaking his whole body after a walk — that vigorous shake starts at the head, and dogs with neck pain abandon it first. Eating can change too: bending to a floor-level bowl may become reluctant work, so he eats a little and walks away, or braces his front legs oddly as he lowers his head. Raising the bowl temporarily and watching whether eating improves is a useful observation to report, though it is not a fix for whatever he has jarred.
Posture, gait, and pain signals
Look at how he holds himself standing still. A dog guarding his neck tends to stand with his head carried low and his neck level with his back, turning his whole body to look at something instead of turning his head. Stiffness is usually worst after rest and eases slightly once he has moved gently around, the opposite pattern from simple tiredness. Yelping when a collar is clipped on or pulled, crying when lifted under the chest, trembling, panting while resting, and uncharacteristic grumpiness when approached are all pain speaking. Check his walk on a short lead on flat ground: scuffed front nails, paws that fold under, or a wobbly, uncoordinated hind end after a spinal jolt are more serious signs than stiffness alone.
Resting him properly from tonight
From the moment you suspect the jump hurt him, the routine is restriction. Lead-only toilet breaks in the garden, no stairs where you can avoid them, no jumping into the car, onto furniture, or after toys, and no rough play with other dogs, whose invitations he may accept despite the pain. Swap his collar for a well-fitting harness for those short leads so nothing pulls on his neck, and lift him into the car — supporting chest and hindquarters together — rather than letting him repeat the jump that caused this. Do not give him human painkillers from home or leftovers from another pet; several are dangerous for dogs, and masking pain can let him move in ways that worsen the injury.
The signs that mean same-day, not wait-and-see
Some post-jump signs should never be monitored overnight. Weakness in any leg, dragging or knuckling paws, an unsteady or crossing gait, inability to rise, crying out repeatedly, or loss of bladder control all point to possible spinal cord involvement and need a vet the same day — immediately if they are progressing. A dog who was merely stiff at lunchtime but is wobblier by evening is deteriorating, and that direction of travel matters more than how mild the first sign seemed. Keep him as still as you can for transport, support his body on a firm board or blanket stretcher if he cannot walk steadily, and ring ahead so the practice expects a possible spinal case.
At the vet, and recording what happened
Tell the vet the specifics: the height of the boot, the surface he landed on, whether he slipped, and the first change you noticed and when. Those details shape what the vet checks far more than 'he seems sore,' and the progression since — better, worse, or new signs — guides whether rest is enough or imaging is needed. Writing the incident, the signs you observed, and the vet's findings and rest instructions into his KinsLe Pet Passport keeps the episode documented in his records packet, ready if stiffness ever returns and a comparison with this episode matters.