Basically the server crashed, quickly followed by the other Euro servers, they are still trying to fix it 6 hours later.
It will mean a roll-back, ie. they will make the server restart from a point in time where it was working, so if you were on lava 10 mins before the crash you might log in on it, but not on a mount, and you will be dead! etc. etc.
Not that the above situation descibes Jibbletts woe (probably)
Double Experience Points (XP) For European Servers
Due to the recent downtime with the European servers, Infinity, FarStar, and Chimaera, we will be enabling double XP gains on these servers. Once those servers are brought back up after the scheduled maintenance on Sunday October 30th at 3am GMT, all XP that is granted on these servers will be double the normal XP rate.
This will continue until our maintenance window on November 3rd at 3am GMT, at which time XP gains will return to their normal rate. Thanks again for your patience during this time.
We apologize for the inconvenience and appreciate your patience.