How do you know when your an empath?

Well, lately I've been feeling severly drained, as if I don't want to do anything. But then I'll get sudden bursts of energy, which don't last long. It happens when I'm with certain people though, different kind of friends and family... it's odd. I'm getting better at controlling how I feel throughout the day, but it's like second nature to me, and I guess you could say I feel like a chameleon. What's going on?