Water changing may play a part in his stress too, mine get changed once every two weeks (which is when the water gets cloudy). They aren't really like turtles where they need constant changes. And most fish will freak out during water changing because they are being moved around.
One thing you can test and it's said to be good to do this once in a great while (I don't know if it's true or not, but I do this like once every three months) is to get the betta to puff out and show his aggressive side. (Ice though does this everytime someone walks by) They say it's good for the fish because it gets them active and moving. So what you may need to do is get him to puff out (by this I mean where he moves his gills outward so that they stick out from his sides and make him look bigger) Though I wouldn't try this right away. But I know that a sick betta will not puff out. (Patrolman didn't puff out when I noticed he was getting sick) Since you don't have two bettas it will be hard to get them to puff out. With Ice though I'll just run my finger along the bowl, chasing him and he'll puff out. (some fish will hold the puff out for a while, others like Ice, it will be quick)
And also he may just be acting like himself right now (though I know it's not what you said he was acting the week before) but I know that Patrolman would hardly ever swim around after about a month of being in his bowl, he would just rest on the bottom and sit there till it was time to eat or breathe. So your fish may have just adapted and realized that there is life beyond the walmart betta death bowl, which could also be a part of why he was so active the first week, he was in a bigger environment and wanted to play. Now the environment is kinda old school and he used to it so he can relax now. Ice did this when I got him, at first he wouldn't even go lower in the bowl, he would just sit near the top thinking that was all there was to it. I finally gave him a little shove down and he realized that there was more to it and he wouldn't stop swimming around for about two weeks. Now he's calm and just hangs out wherever he wants, though sometimes he will go into his fits of swimming around like a mad man.
Also signs of a heathly/happy fish are the "bubbles" I told you about. (fair warning some fish, like Ice..eat those "bubbles" so you might have a hard time catching them) if there are "bubbles" around the edge of the water then your fish is fine. If not that's still normal too, the "bubbles" just mean he's really happy and really healthy. If Ice produces "bubbles" anytime soon I'll try and get a picture up. I know yesterday he did but by the morning he ate almost all of them. (he's the only one I've had to eat them....and I don't even want to know why cause he gets feed plenty.)
Here is a website that will explain the "bubbles" a little bit.
http://www.betafacts.com/betafishmating.php and show you a little picture of them (though I believe in that picture there are eggs in the bubbles) and from what it said there bettas are kinda used to their fins getting hurt a little, so I would give your guy a few days and see if he livens up, and this may just be his new relaxed behavior since he realizes that no one is going to send him back into a tiny little bowl.