I think I've accidentally overfed my betta, and now he is experiencing some issues with keeping himself upright. I did some research and I am happy to know that the bulge on his sides right in front of the caudal peduncle is his swim bladder and that it is how it is supposed to look, supposedly. His stomach is very slightly distended so I'll fast him for about two days to see if he will look and act any better. I haven't seen him defecate at all either so that should be another sign.
But, on a happy note, I've actually been able to watch him make a bubble nest! It is simply amazing - he takes a huge breath of air and then deposits some bubbles under the mound he's made already. Really exaggerated body motions to go with the air gasping as well. It was really surprising to actually be able to hear the sucking noise through the tank walls (with a full cover on), and despite someone's muffled music playing down the hall. Each time he took a breath his back arched inward and his head went upward to the surface. It looked like was having convulsions, but thankfully it was not the case.
I also found out that he does not like to build his nest while the light is on - he was pretty perturbed until I turned it off when he continued on his merry way. This is so exciting - only 5 days and he is already making nests! I feel happy about that.
Does anyone else have fish that are very secretive about their nest-building?