Kidney stones can be both paroxysmal and painful all the time, which is related to the size and location of the stone as well as the hydronephrosis. When kidney stones are small, they can become lodged in different parts of the ureter as urine is passed. When embedded in the ureter, paroxysmal colic will occur, which is usually severe and requires emergency antispasmodic pain relief. However, when the stone is large, hydronephrosis will occur, and there is no symptom in the early stage, but with the aggravation of hydronephrosis and the increase of the stone, there will be continuous dull pain, and this pain is not severe.