Can you be okay one minute and in labor the next??

Has anyone been told that they're not even close to having their babies and then had them earlier than expected? I am 32 weeks with b/g twins and told my cervix was very long. I have had no contractions and told I am carrying very well. When I was pregnant with my son, I was told the same thing when I was 4 days past my due date at 10am....by 5pm I was in full blown labor.