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1.
The 2-3 hours that disappear while you're out enjoying yourself in a bar and then get added on the next morning at work between 9 and 11.
"Jeez, the morning really dragged! Must be Beer Lag from last night."
by Expat Mat March 09, 2007
 
2.
The delay that occurs between thinking something and typing something after you have been drinking.

Not sure what anyone else would call it but I coined the term after getting home around midnight and attempting to post on a forum.
Thinks: 'Hello'
around about half a second to a second later the fingers type: 'Hello'
by Glen Mailer September 05, 2004
 
3.
Biologic-clock disorder produced by staying awake drinking beer till late. Deduced from jet lag which is the same effect but produced by east-west long airplane travels.
Aida: Good morning Marcos, already at workplace?
Marcos: Late again, I oversleep cause I'm under the beer lag.
by Marcos Mayorga November 26, 2007