Originally Posted by tracyalexa
Especially if I have two with a divider? Why is that?
IMO betta's use up quite a bit of energy to flare and all that. Their muscles work spontaneously at once. If a betta can constantly flare, he will 1) eventually be come tired. Or 2) he might realize that it's useless and loose interest until he feels threatened. And last possibility; 3) if he has poor mentality, he will become scared (stressed) and will not flare again - specially to the same color as his rival.
Your betta sounds as if he would still flare but he doesn't have the energy - he rests on the bottom. If he were experiencing the 2nd or 3rd possibility, he would simply swim away.
If my assumptions are right, you should be worried. Again, IMO, a non active betta has low immune abilities (I don't know why). So be sure to keep an eye on him.... hope I'm wrong.