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.
National Sleep Foundation Updates Recommendations For How Much Sleep You Really Need. Some of us feel well-rested after a solid eight hours of sleep. For others, closer to nine feels best. For others still, a little less will do. How much sleep we prefer to get is highly subjective -- but how much sleep we need is a bit more concrete.