Extreme sleepiness

I don't know what is my problem.

It is not like I lack that much sleep ~ I have been sleeping relatively earlier nowadays. And yet, I have been having extreme sleepiness throughout the day, for the past week. I am so sleepy that I can't think straight when it comes to writing my papers. I have to work out of the home, or I would gravitate toward my bed.

I so need a nap.