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1.
When you've had a late night out getting drunk but you wake up early with seemingly a ton of energy. So you get up and go about your day only to suddenly feel a huge energy drop, normally after you have eaten.

It's essentially a late hang-over.

(Pronounced False-E or False-E's)
Tom: "I was out really late last night with Dan and Gary but I woke up super early and I feel brilliant"

Dan: "Nah, mate. Don't fall for it. You've got the falsee's!"

....2 hours later

Tom: "I'm feeling so drained, I need to sleep so bad."

Dan: "Told ya it was a falsee!"
by Dandonian December 08, 2012