Normal activity for a dog includes greeting, investigating, guarding, playing, and sleeping. Most activity is spontaneous, but some are encouraged by the guardians, such as going for walks, playing, etc. Dogs that are suffering from disease tend to withdrawal from their usual activities and spend more time resting and sleeping.
Changes in activity levels are not specific to a given disease, but are an indication that something is awry with their dog. It could be something as simple as a response to high ambient temperatures to an indication of more serious illness.