What Could Extreme Fatigue And Nausea Indicate?

The last week or so I've been extremely fatiqued & nauseous. I do take several meds for chronic pain. But I've taken these for sometime now. What could be the cause of this? Also when I say fatiqued, I don't mean just a little
tired, I'm so sleepy I can fall sound asleep in just a few minutes if I'm still very long (like just watching TV for a couple of minutes).