Is my betta depressed?

[bounty]

I've had my halfmoon, Venus, in this 5-gallon tank for over a month now, and I've noticed a change in him. He used to be super active, darting and swimming everywhere, but lately, he's been swimming really slow and just kinda floating around. He doesn't appear to be sick or anything, just not as lively as he used to be. Maybe I'm reading too much into it? It's just him and two snails in the tank, and I've been hesitant to add other fish since he's pretty feisty. I'm thinking of upgrading to a 10-gallon tank because I feel like he needs more space, but that won't be for another month or so. My water parameters are all good - ammonia and nitrite are 0, and nitrate is under 5. In the picture I posted, he's at the bottom, but that's not where he stays all the time, he likes to just chill on the plants or in his house.

[SeaBidder]

I've got a few halfmoons that just kinda chill most of the time. They're not really big swimmers, just kinda cruise around every now and then. I've got a couple that are always building bubble nests, but the others, yeah, they're just pretty laid back.