When you have so much sex and get so worn out from it that your bodies internal clock becomes messed up and you feel tired all the time.
I am so sex-lagged from this weekend with my girl.
That two-three day lag which one exeriences after a long weekend of debaucherous sex. Generally it takes a couple of sleeps and a long shower or two to get over it. One of the grimiest ways you can ever feel. Spent.
"I'm sorry Joe, can't come out tonight due to extreme sex lag, need to get some sleep real bad or my brain won't turn on again".
The fatigue and mild sense of disorientation experienced after staying up all night having sex, thus disrupting the body's circadian rhythms as would an international flight. Also shag-lag
"Man, I don't know how I'm going to stay awake for work Monday, I've got serious sexlag from Saturday night."