Opinion:
In my opinion it's not being free and being forced to work against your will but...
Honest answer:
One of the most cruelest parts of slavery were the punishments slaves received during slavery. Slaves were punished by whipping, shackling, hanging, beating, burning, mutilation, branding, and imprisonment.
Punishments were given to slaves if they were disobedient towards their masters. Sometimes abuse was performed to assert the dominance of the master over the slave, meaning that some slaves received punishments for no reason at all-- they were received it to be obedient and to invoke fear of their masters.