Your dog is asleep on the sofa. Someone brushes past, they wake with a growl or snap and then seem surprised to see you. That can be a startle response, not a planned threat. The distinction does not make it safe to repeat.
Give your dog a quiet resting place away from foot traffic. Teach children and visitors to leave sleeping dogs alone, even if their eyes seem partly open. Do not touch them to test whether they are awake. If you need them to move, speak from a distance, wait until they are alert, then invite them over. Never bend over a sleeping dog or reach into their bed.
Make rest predictable
Consider where the reaction happened. A dog sleeping in a doorway, on the sofa beside a busy family, or near another pet may be startled often. Move their bed to a calmer spot and make it a place where nobody bothers them. A gate can help keep children or other animals away when the dog rests. A crate can be an option if the dog has already learned to like it, don't shut a frightened dog into a new crate as a quick fix.
A growl is information. Punishing it can make warnings less obvious without removing the fear. If your dog is newly reactive, older, hard of hearing, painful, or confused after waking, book a veterinary check. If there has been a bite or children are at risk, keep them safely separated and get individual guidance from a qualified behavior professional as well.
You do not need to teach a dog to accept being disturbed in deep sleep. You can make your home a place where they don't have to.
Sources: Battersea: Sleep startle in dogs. Dogs Trust: Resource guarding in dogs (safety around resting places).