This is obsession on one single thing. Just one. A single solitary thing. It becomes all-consuming, and you can think of nothing else. Yes, one thing and only one. A concentrated point, like a target that cannot be avoided. One and only one thing. A sole specific *BANG!* (sound of someone blowing smoke off the barrel of a gun)
See the article on OCD, Make sure you read it carefully. Then read it again to make sure you have all the points down. Then read it again to be doubly sure. Then read it a third time. Then read it again. Read it againandagainandagainandagain.
There is no such thing. It is perfectly normal to be thinking about sex 24/7, 365 days a year, 366 on leap years. So just take off your clothes and come over here. Never mind, I have my hedge clippers with me.