Fish Swimming Vertically

I've searched all of the related material I can find, but nothing
seems to really explain why my african cichlid is doing this...

it choses to swim vertically up against the aquarium heater. It has
been doing so for several weeks now. It's eating normally, but once
it eats it goes right back up against the heater. The temperature of
the tank is fine, Ph is good but I'm kind of at a loss