Loss of balance can be caused by many different problems. Balance and coordination are controlled by the inner ear and brain, problems with either of these areas could cause balance issues.
If your dog has less energy than normal, we call it lethargy. Lethargy with no obvious cause usually indicates a problem.
Mites and lice are tiny parasites that like to live on dogs (and other species). They damage the skin by biting or burrowing and often cause intense irritation.