Why Does My Dog Have Episodes Of Falling, Bumping Into Things,shaking,and Stiffness?

I am concerned your dog is having seizures or partial seizures.  Other concerns would be episodes of hypoglycemia (low blood sugar) or syncope (a cardiac problem leading to collapse).
Have your dog examined by a veterinarian to determine the cause of these episodes and start treatment.  Bloodwork will be run to screen for various diseases and causes of seizures.  Chest x-rays may be needed if your veterinarian feels this is cardiac in nature.  
If an episode occurs before your appointment try to videotape it to show your veterinarian.