A brief, transient peak in alertness occurs in the evening hours before the circadian system downregulates for sleep.

“right before sort of bedtime there is this sort of strange little blip this peak um that Folks at um back at Harvard have have discovered and you think well why would my Cadian system which needs to really ratchet down for us to get to sleep well why would it have this little Jag upwards in the evening hours right before we need to sleep and it then drops precipitously right makes no sense until you think about Evolution because after foraging for food during the day what you need is this final spurt to get you home safely to your nest or to your home”