I had painful ones the other morning, and i still get them since then, but this one particular morning it was so bad.
I dont know exactly how long i had them for, but it was well over an hour. i had 'normal' period pain, but every 5 or so mins id get a tightening and the period pain would be so painful, and would wrap right around the my lower back as well. I was literally doubled up in pain.
If your concerned maybe call your MW or OB??