The slightly swollen stiff area you mention is likely caused by inflammation/irritation due to toxemia, but can be caused by injury or other injurious stimuli.
Without inflammation, infections would go unchecked and wounds would never heal. Damage to our tissues and organs would ensue and cancer would be more likely to occur if the body did not diligently attempt to remove toxic substances from its tissues. It is common to think of bacteria/viruses as the cause of inflammation, but almost all other causes of cell injury also provoke inflammation, including localised toxemia.
There is nothing more effective at eliminating the root-cause of inflammation than a water-only-fast according to thirst, and thirst only.