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That time at night when working late that you and your coworkers find even the stupidest things hilarious, as if under the influence of drugs or alcohol.

Typically induced by working extensively all day or being at work late at night.
Steevn: 2nd Shift Fever was bad last night.

Sally: Yeah, we laughed at an umbrella for like five minutes.
by Megaman31291 May 23, 2011