Why does my dog pace at night?

This excerpt is from ASCPA. Restlessness/Waking at Night Dogs who sleep more during the day can become more restless and active at night. Some dogs start overreacting to things they once ignored, like the garage door opening or the newspaper being delivered. Keeping a record can help you identify what triggers your dog’s nighttime activity.

Sensory changes, such as eyesight or hearing loss, can affect your dog’s depth of sleep. His sleep-wake cycles may be affected by cognitive dysfunction or other types of central nervous system disorders. Ask your dog’s veterinarian to do a complete examination to look for medical problems that could cause restlessness, discomfort or an increased need to eliminate. Any medical problems should be treated first, and then, if necessary, you can gently retrain your dog to reestablish normal sleeping and waking hours. Try increasing his daytime and evening activity by giving him frequent walks, playing his favorite games, practicing obedience or tricks, and giving him food-puzzle toys and bones to chew. You can also ask his veterinarian about combining your retraining with drugs to induce sleep or, alternatively, drugs to keep your dog more active during the day.
https://www.aspca.org/pet-care/dog-ca...

Some other reasons include: loneliness (especially if new puppy), pent up energy, nocturnal critter, emotional turmoil, physical issues.

If your dog is pacing at night, there could be a couple of explanations. Firstly, if your dog is a senior (7+ for large and medium breeds, 9+ for small and toy breeds), he could be experiencing mental confusion or a cognitive impairment. Sometimes, when dogs age, the chemical imbalance in their brain becomes offset, causing them to forget things or to not feel sleepy at night like they used to. While a visit to the vet is advisable if this becomes an ongoing occurrence, it may help to create a bedtime schedule/routine for your dog or to use a pheromone spray to calm him down before bedtime. If your dog isn't a senior, he may be feeling anxious or is in pain. If his pacing is continuous, a visit to the vet is advised to rule out any other health conditions. The vet may also be able to prescribe a mild sedative or anxiety reducer to help your pup get a good night's sleep!