You should be able to rejoin at some point - again, if the server has a forum, I'd take a look there - it may be an hour or two. Meanwhile, a few questions:
(a) Which server?
(b) Where are you based (country)?
(c) If you run this:
http://www.pingtest.net/, what results do you get?
(d) Are you using WiFi to connect to the net, or a cable?
(e) Are you sharing your connection with anyone?
This might give a clue as to the problem.