Doubt in salah islam

"If during prayers one does something or remains silent for a while and doubts whether or not his prayer has broken up, he must perform the prayer again. However, it is better that he first complete that prayer and then repeat it." Now after reading it I have a question that if I doubt that whether I laughed in salah or not or some other doubt like that so it is must for me to pray again? Please explain the above statement from an islamic site