This Thursday the 9th, BioWare will take down the Star Wars: The Old Republic servers to perform unscheduled maintenance. During this window, servers will be offline but will return with the need to download a patch.
After the maintenance, please login via the launcher to download the latest patch. If your launcher was open during the maintenance, you must close and reopen it for a fresh login.
To find out more about this unscheduled maintenance window, head on over to the official post.