My Male Molly Is Acting Weird

[minirhyder]

He swims around, then all of the sudden he stays in one place, then turns himself vertially (head facing up) and swims like that for a couple of seconds. Then comes back to normal horizontal position, and then repeats it a few times.

What's up? 0.o

 

[wei0204]

He is either under pressure or sick....

 

[minirhyder]

He shows no outward signs of any kind of sickness.
What kind of stress could it be?
My pH is 7.1 or so, and my ammonia is 0. The temperature is 79.