Last week mine did that once. I was feeding him and he ate the pellet. all of a sudden he went straight down to the bottom of the tank. I thought he died. After a few seconds, felt like minutes he started swimming again. The only thing I could think of that made that happen was maybe the pellet got stuck in his throat. Hasn't happened again and I hope it never does. He really scared me.
I think of it more as a hunting type behavior. Mine will freeze when he is stalking live food. He goes motionless, all fins stop movement, and he drifts, but I see his eyes, following the live food. And then he jets off after them after a bit. I think in nature they'd have better camouflage with their coloring so I think it is a stalking, predatory type behavior, especially since it occurs usually with feeding apparently.
I've had a cory that would "faint". He'd be fine and swimming around then all of the sudden would kind of spasm out and drop to the bottom and lay on the sand motionless for a few minutes. Then would seem fine. It was something neurological because eventually he died.
I also had a Congo tetra that fainted when the fish shop guy netted and bagged him. He was upside down in the bag and I mentioned something to the guy and he said "oh, they do that all the time. He'll be fine." And he was. Still have him today. Posted via Mobile Device
So, if a fish can faint, can they also have narcolepsy? I swear my male is narcoleptic. He'll swim around normally, then suddenly stop in mid-swim, and looks like he's sleeping. He doesn't fall to the ground, or float to the top, just stops, like he's completely frozen in place. He's completely unresponsive during this time. He's also a VERY heavy sleeper, and it take quite a while to rouse him in the morning or when it's obvious he's sleeping for food.
Well considering fainting is caused by neurological impulses and or lack of blood flow to the brain. since fish do infact have brains, it's completely possible that they can faint. It's also possible that when he swam fast to get the bloodworm, he could have been spooked by something. Maybe a sudden reflection, or his fins hit something he wasn't expecting, which could all cause him to go into a shock state. Like how when you spook a hamster they suddenly turn stiff for a moment, then start to move like normal.
You could just have a very skittish betta, or something just spooked him that time. If he's fine now, he should be alright.
It could be a self defense mechanism. If the fish is being caught or realizes it may may have just compromised its camouflage it could be trying to protect itself. This could be the fish trying to blend back in with the *non-existent in some cases* surface debris or foliage to mask the sudden movement it just made to prevent other "prey or predators" from detecting it. Seems a little more reasonable and universal than a seizure or a stroke. On the other hand some of these pet store fish don't have the best genes... Anyway these are just speculations no real evidence to back it up so I guess we'll never really know.
Well with an animal this small the difficulty is rather large, you could try and recording behaviours, factors possibly affecting behaviours and set up a whole experiment. The most thorough way would be an autopsy of the brain for abnormalities or defects *once the fish is s.i.p." but the cost of the equipment and just to find out if it's neurological or instinct would be rather pointless *to say it bluntly*. I guess it would be a good experiment for a university student who has access to the equipment though .