it could be a couple of things bloat which is over feeding or taking in to much oxygen when feeding, or carrying eggs.
courting, are the two fish chasing one another usually into a plant (or spawning mop)
is there any sign's of little white dots on the gill plates showing signs of maturity if not then you could rule out spawning,
have you tested your water because sometimes bad water conditions can make a fish dart about rubbing and flashing its dorsal fin
try a 25% water change with dechlorinated water if the darting about stops you know it is a water quality issue
hope this helps