How often are you changing your betta's water and what type of container is he in?
Many things can cause a betta to lie listless on the bottom of his container.
The primary consideration is water foulness. If ammonia and fish waste (feces, rotten food) are allowed to accumulate in the water, they can poison the fish slowly over time to the point he is depressed and will eventually succum to the toxic stuff. With bettas in unfiltered environments, no matter how large, a 50% water change should be done every day, usually it is best to do so after a feeding so any uneaten food can be removed from the container.
The second consideration is water temperature. Fish become depressed in lower temperatures as their metabolism slows down. Anything below 68oF might be harmful to your betta. Also extreamly high temperatures can be dangerous. Anything above 84oF can make a fish spaz-out.
If extream temperatures and water quality can be ruled out, the third and most contrivertial explaination is simple depression. Male bettas that do not have anything to flare at once and awhile sometimes become depressed. Place a mirror near your bettas tank for perhaps ten minutes a day and watch him flare and dance at his reflection, trying to chase off the "rival" fish. When you remove the mirror, you betta perceives this as a dominate victory, and it may help improve his mood a bit and increase his betta self confidance.
It is very common for male bettas to spend a majority of their day resting, either on the leaves and within the plant decorations, or on the bottom if there is nothing else (mine "sleeps" inside a coffee mug in his tank<G&gt
. They have such long finnage that it makes their swimming cumbersome and expands alot of energy. Feed your betta as you are doing now, one piece of food at a time, and make sure he eats each previous piece before you put in the next one. Usually 4-6 pellets is enough. I would also increase to feeding your fish twice a day. You can tell when a betta has had enough food by how swollen his belly will be (in the spot directly behind his pectoral fins) when he is done eating. My betta has taken up to ten pellets if I have felt especially generous in spoiling him.
Good luck and I hope this helps.
~~Colesea