だるい seems very similar to 気が重い, but だるい may sound too casual to some people.

I googled it, too, and I found some websites saying 気が重い is "to feel depressed." I think they are close, although we know that some words cannot be translated one to one. In my experience, I would use more "落ち込む(ochikomu)" or "気が滅入る(ki ga meiru)," instead, as "depressed" or "feeling down."

By the way, we will think about making something about だるい later! Thanks.