Circandian Rhythms In Our Daily Life

I have been going through the  Exams in last Couple of Weeks, Have Taken half of my Exams and Half are on the way.   This Talk started when we had just Taken our Biology Exam and Written a short Question On Ciracandian( Bilogical Rhythms which repeat itself daily with exact time) and Circanual Rhythms( bilogical Rhythms which repeat themselves Yearly ), One of my friend said he has been noticing this rhythmic Clock (  Circandian is Biological Clock Phenomena which repeats itself on Daily Basis in Our Life ) due to his self …..x practices. I mean he did it one day, Experienced the need to do on the other day at same time, He did it again but the Next  day he was feeling it again ( The  ….st ).  As mysterious as it is, I strongly beleive that it happens with everyone ( Experimently Prooved by Biologists ). So we want to do that self …..x thing whether you are girl or a boy it will not your ………… down but it will only increase your Lust for it. I wonder if you have Experienced the same Thing Before???