Maintenance for the week of April 27:
· [COMPLETE] EU megaservers for maintenance – April 27, 2:00 UTC (April 26, 10:00PM EDT) - April 27, 16:00 UTC (12:00PM EDT)
· [COMPLETE] NA megaservers for maintenance – April 27, 3:00AM EDT (7:00 UTC) - 5:00PM EDT (21:00 UTC)
It think it happens when there is some type of crash on the "shard" you were on. When you login again your characters likely "moved" to a working shard but a few minutes of loss in progress seems to be the result.
This has happened a few times for me as well, but compared to the loss others have experienced, I've been grateful it is only about 5 minutes of loss.