Erf... having no energy is probably a sign that your body's using it all to fight off whatever's doing this to you. It's not pleasant, but hopefully it's not a sign that the train's coming for you. Just take things slow; get plenty of sleep even if it means taking lots of naps, eat well, drink some Lucozade (or your energy drink of choice) if you really need to do something, but otherwise, just rest yourself.

*hugs gently* Get well soon, man.

D.F.