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1.
Call it what you want, but "Mondayitis" is a feeling of weariness, sadness, apathy and general distress that many individuals feel when starting the Monday morning work week. This feeling is usually enhanced after a large weekend.
Boss: "good morning, looking a little worse for wear whats wrong?"

Worker: "Got a case of Mondayitis"
by Domin8or November 18, 2007
 
2.
The seemingly contaigous disease that effects people on Mondays. Symptoms include not showing up for work or even calling in, usually triggered by over celebrating Sunday Funday. Home cures include late night breakfastses, sleeping late and half-hearted pledges of sobriety. Usually lasts until Friday Eve.
whenever i celebrate sunday funday, i usually end up with a bad case of mondayitis!
by duffball October 22, 2009
 
3.
when you feel tired and grouchy on a monday because you have had a rough weekend usually with little or no sleep
darn this mondayitis i feel so tired
by -cliche- October 30, 2007