Mexicans were treated just as badly as anyone else who was enslaved in America. They were beaten and forced to work. The term slavery denotes harsh cruel treatment and forcing people to work for them for free. Anyone no matter where they came from was treated poorly if they were a slave in America.
The only way and the main way to not be a slave was to escape to the north. I believe Mexicans if they were enslaved would most likely return to Mexico if they cut it. Slavery was eventually considered illegal but people would still try to enslave people against their will. It took a long time for slavery to end in America do to the economy.