I have quite a lot of energy, but I know some people just aren't as lucky. Is their a medical condition for being constantly tired?
I think it's called Chronic Fatigue Syndrom, or CFS.  I don't know a lot about it, but it makes people tired for long-term amounts of time.
That must be awful. I wonder what causes it. Depression perhaps?
I don't think the cause is fully understood.  It could be genetic, could be biological, or it could be psychological.
Well, I guess the medical profession had better get to the bottom of it. It must be destroying people's lives!
I'm sure it is, but people are starting to see that behavioral therapy and a slow increase in activity can help counteract the effects.
That makes sense. If a person exercises it often brings ones energy levels up.
That seems to be the case.  It also looks like evidence has shown that there's no adverse effects from trying to counteract the effects of CFS, which is good.