Flashback feature in Oracle 11g?
Firstly, you must enable flashback. In SQL*Plus as SYSDBA:

shutdown immediate;
startup mount;
alter database flashback on;
shutdown immediate;
startup;


Next before your load operation, create a restore point:

create restore point before_load;


Now do you work, and when you're done:

shutdown immediate;
startup mount;
flashback database to restore point before_load;
shutdown immediate;
startup;


And your data is back as it was. You can repeat this as many times as you like, and when you are done, drop the restore point. HOWEVER the commenters are correct; you should leave the constraints enabled and just defer them.