I don t drink caffeine like coffee only when I want to stay late. I don t know what hit me last week. I feel progressively sleepiness, lack of energy and tiredness. I tried to drink coffee but no use. I tried to go out and walk. But I felt I would fall asleep in any minute. Thus in a minute, I walked back home immediately. Driving is also extremely difficult because of the sleepiness. What I wanted is go sleep. I don t take drug. I occasionally take multivitamin. That s. Because of this tiredness and sleepiness, I didn t go on my daily routine: an hour morning walk. In the first 2 days, I tried to stay awake a few hours but the 3rd and the 4th days, I could not and I slept all the way. 48 hours without waking up or eating. On the 5th day, I gradually woke up but I still felt very sleepy and extremely tired. Anyway, this sleepiness and tiredness went away in a few days after awake finally. Now I am energetic and everything is back to normal. I have no problem to get up at 6AM for my morning walk and stay awake until 11PM when I go to sleep. Should I have to worry about it? What caused it? I tried to search around on the Internet but I cannot find a hint.