It's not so much about being exhausted, as me being unable to use two different abilities at once. Usually I would be able to maintain something as minor as keeping my appearance up regardless, but I am rather weakened.

[He inspects the trident once more, making sure it's in perfect condition. Satisfied, he holds it upright paying attention to Zuko once again]

My body will recover in time, however I refuse to be flopping around uselessly like a newborn infant until it does. Surely you can understand.