Chronic pain is an unpleasant pain, that is nagging and uncomfotable. Chronic pain can last weeks, even months. Chronic pain often is caused by actual or potential tissue damage, the clincher is that even if the tissue heals, the pain my continue or even worsen. Now Acute pain stems from actual or potential tissue damage that improves as the tissue damage heals.
According to the American Academy of Pain Medicine, as of 2011 at least 100 million adults Americans (we're talking close to half the adult population) had common chronic pain conditions. The direct medical costs and economic costs for lost productivity from chronic pain on this many people ranges between $560 billion and $635 billion annually (based on 2010 dollars), which works out to nearly $2,000 for every man, woman, and child in the United States.