Normally your bladder gently fills with urine and you slowly become aware you have to go. People with bladder spasms get this sensation suddenly and often severely. A bladder spasm, or detrusor contraction, happens when the bladder muscle squeezes suddenly without warning, causing an urgent need to pee. The spasm can force urine from your bladder, causing leaks. When this happens, the condition is called urge incontinence or overactive bladder. People who've had them describe them as a cramping pain and sometimes as a burning sensation. Some women compared severe bladder spasms to severe menstrual cramps and even labor pains.