There may be several reasons why dogs sleep so hard:
Dogs need more sleep than humans. Dogs sleep approximately 12-14 hours per day, compared to approximately 7-9 hours per day for adults. Therefore, when dogs sleep, they may enter a deeper sleep state that is more difficult to wake up than humans.
When dogs sleep, they secrete chemicals such as dopamine and serotonin in their brains. These chemicals make dogs feel comfortable and relaxed physically and mentally. This may make it easier for the dog to fall into a deep sleep state and be difficult to wake up from external stimuli.
The nature of dogs makes them like to find safe and comfortable environments. When dogs feel safe and relaxed, they are more likely to enter a deep sleep state that is more difficult to wake up. In short, when dogs enter a deep sleep state, they may become difficult to wake up, which is normal.
If you need to wake your dog up, try gently waking him up with a soft voice. However, if you find that your dog is constantly overtired or sleeps irregularly, or if you notice that your dog is breathing irregularly while sleeping, it’s best to consult your veterinarian.