always swimming up

One of my two lamp eye tetras is doing something odd. It just constantly
swims up. If he stops swimming he sinks like a rock, but it never stops
swimming straight up long enough to sink all the way to the bottom to just
lay/rest there. It's like he's swimming head first into a strong current...
constantly. He's eating and otherwise looks normal. Has been going on for
about a week and no other fish in the tank are doing this.

Is there anything I can do for him?

Thanks for the help,
Lydia