what happens to the mind during meditation? l experienced stopping of thoughts comes to the mind at a point  and starts again.During that time my breathing has completely stopped.it is like mind has stopped for a moment.could that be possible?
This experience is called Asanna in Buddhist meditation. (see no 22 in the link)
Please make sure you practice this meditation in conjunction with Vipassana meditation.It also advisable to practice meditation in conjunction with Noble Eightfold Path.  

http://www.accesstoinsight.org/ptf/dhamma/sagga/loka.html