Other safety precautions are that you should never massage a dog that is suffering from fever, shock or cancer. Also, as you massage, avoid any areas of unexplained swelling. Also, remember that massage is not a substitute for proper veterinary care, it is a compliment to it, and it has many benefits for their health.
Some studies have shown that your deep sleep should at least be 20% of your overall sleep. It means that since most adults need 8-9 hours of sleep, they will need about 1.6-1.8 hours of deep sleep to feel fully functional next day. However, the time of deep sleep is changed and that's mainly due to the change in the sleep need of different group of people. For instance: Age Group.
The typical person will experience five stages of sleep each night. It takes approximately 90 minutes to pass through all five stages of sleep. According to my mathematics, if a typical person has roughly 8 hours of sleep, then they should also experience five cycles of sleep. That being said, not everyone will experience the same sleeping pattern.