What you can do to help your dog will depend greatly on the reason your dog is falling over, off-balance or uncoordinated.
For example, if your veterinarian determines it is idiopathic or ‘old dog’ vestibular disease, then supportive care may be the only treatment required. Typically this includes anti-nausea medication like Gravol or Cerenia. It may also mean using towels or blankets as supports to help your dog get around for the first few days.
Alternatively, if a more serious condition is diagnosed, your dog may require hospitalization and intravenous therapies (antibiotics, steroids, etc), or even surgery.
In all cases, the first step is to ensure your dog is safe while you arrange to get them to their veterinarian. This may mean blocking off access to stairwells or swimming pools and moving any nearby hazards to avoid potential injuries. They may also do better on floors with traction rather than slippery tiles or hardwood.
In many cases, these dogs are in distress, so being a calm and supportive presence is also important. If you are panicking, your dog will sense this, and it will only make things worse.