What happen to the transactions in the block chains that lose out? Let's say a payer paid me by creating a transaction and broadcast it. That transaction got

What happen to the transactions in the block chains that lose out? Let's say a payer paid me by creating a transaction and broadcast it. That transaction got lumped into the current leading block chain. Somehow another block chain gains and wins. The block chain containing the transaction is discarded. What happened to the transaction? Is it discarded as well? Do I just got unpaid?