Betta out of water for 3 hours

Question
I changed my betta's water right before going out for about 3 hours a couple
days ago. When I came back, I realized that he was no longer in his tank! I
found him behind the shelf that the tank was on, lying on the ground. I put
him back in the water and he started to swim. I know he was lying there for
about 3 hours because my friend noticed he wasn't in his tank before we left
but she thought he was in his little home. The home was just added to his
habitat and I know for a fact that he does not go in there.
It has been two days and he is in his tank - the water temperature is at 75
and I lowered the water level so he can get air easily. He has some sort of
cottony like growth on him and I diagnosed it as Columnaris and am currently
treating it with Tetracycline.
He was doing ok yesterday because he was swimming around but today he is
in one corner in an upright position getting air whenever he needs it and
breathing heavily. The water level is low enough that he can get air without
straining himself. I'm worried that since it was such a long fall from the shelf
to the ground that he has damaged his internal organs.
Do you think that he'll be able to recover? And if so, how does a fish recover
from damaged internal organs?

Answer
Hello Olivia,
I don't think he has damaged his internal organs since he was swimming around yesterday.  (There is no cure for damaged organs)  There is another reason why he is not swimming today.  Be careful not to overdose.  He would have a bad reaction to overdosing.  He is surely stressed from the fall.  All you can do for him now, is keep his water very clean, and make sure you are not overdosing him.
Hope this helps
Lynda