See: jet lag
Australian: It's chat lag, mate.
Chat-lagged: Misinterpreting IM messages because of a altered state of mind.
Chat-lag: The act of replying to IM in a delayed fashion as a result of chatting with multiple people at the same time
"My cool cat buddy in Beijing kept me laughing all night, or morning his time - half way around the world. Now I'm chat-lagged."