Your dog slept through from 5 months old. Now they are up at 3am, whining at the door or pacing the landing. You are back to broken nights and nobody can tell you what changed.
Start with the physical causes
This is one of the behaviours most worth taking to your veterinary practice first. Pain often presents as a change in behaviour rather than as a limp. Sudden behaviour change warrants a veterinary examination.
Ask about 3 things by name: joints, gut and bladder. A dog who needs to empty their bladder at 3am is not a training problem.
Then look at the last 3 hours of the day
For 3 nights, write down what time your dog last ate, last went out to the toilet, and last did something exciting.
Move the last meal later if the waking comes with hunger signs, such as gulping, licking or eating grass first thing.
Add a real toilet trip at 10pm or later, on a leash, in the dark, with no play. Two minutes out, then straight back in.
Finish tug, fetch and wrestling 90 minutes before bed. A dog who falls asleep high wakes easily 4 hours later.
What adolescence changes
Daytime rest is often the thing that has quietly disappeared. A dog woken every 20 minutes by the traffic of the house is not resting, whatever the total hours look like.
Adolescent dogs also go up quickly and have no practised route back down. Relaxation is trained as a behaviour in its own right, in short sets, below the point where your dog gets restless.
What to do at 3am tonight
Go to your dog without talking. Take them out on a leash for a toilet trip, then back to bed. No food, no play, no conversation.
If they wake and do not need to go out, sit nearby quietly until they settle, then leave. Being dull is the whole point.
Do not bring them onto your bed for one night only. One inconsistent night is more confusing than either answer used every night.
You can move their bed into your room for a fortnight. Do it on purpose, and move it back a foot at a time.
If the waking is about being alone
Some dogs at 9 to 14 months start waking because being on their own at night has become hard. That work is gradual, sub-threshold departure practice, and it belongs in daylight rather than at 3am.
In the meantime, sleep in the same room as your dog. Nothing is lost by removing the problem while you build the skill.
Safety note
Get help now if the night waking comes with panic, howling, destruction at the door or self-injury. That needs a veterinary examination and a qualified behaviour professional. Speak to your veterinary practice the same day if your dog seems disoriented, or is drinking much more than usual.
How long this takes
A cause you can name, such as a late walk or a missed toilet trip, often changes things inside a week. A waking habit with no cause left in it takes 3 to 4 weeks of the same dull response.
Tonight's version, in one line: nothing exciting after 9pm, a leashed toilet trip at 10pm, and no conversation at 3am.