Multiplayer error on minecraft multiplayer server

Ok so i logged on to a minecraft multiplayer server (worldofkeralias) and um when i moved my character shaked violently and in chat i saw people disconnecting and reconeccting over and over again, so finally i disconnected from the server and got a error message saying To many packets? (Extreme Lag?) and what i want to know is why is this happening? (notihng close to this has ever happened before)