Is it possible to have a perfectly healthy budgie that just enjoys sleeping?

My newest little guy (or girl) Chicklet, is about 9 months old and is very quiet. I have had him for about 4 months. My other guy sings all day.

I took them both to the vet for a check up. They both seem fine. Weight was good, poops look good. I told the vet that Chicklet seemed a little sluggish lately, quiet and sleeping a lot, so he started him on Baytril for 10 days, just in case he was coming down with something. He has been off the Baytril now for 4 days. His appetite is great; eats seed mixed with pellets (mostly seed) I haven't gotten him converted over yet. He loves green vegetables, though!

He eats like there is no tomorrow then goes back to his perch and sleeps. Any thoughts? I really don't want to stress him out by putting him through all sorts of tests. Just that one trip to the vet really stressed him out.