3 year old Betta Fish, water Temp 70-75 degrees

Question
I have been doing some reading, and I am at a loss as to what is wrong with him.  
While I was on vacation for a week, my fish didn't get fed AT ALL.  The pet sitter was thoroughly reamed.  He is floating at the bottom of the bowl, like he is sitting on his tail.  Not sideways or upside down, put almost straight up and down with his tail at an angle.  He doesn't seem particularly bloated.  He will swim to the top and eat baby pellets, but he has a hard time eating regular pellets.  He will grab those and then spit them back out.  When he swims to the top...it's almost like he has a hard time moving his tail.  His feces looks a little reddish.  I have been doing a full water change every week using Ozarka water, and partial changes every other day or so.  I thought about trying the fasting/pea treatment, but he seems weak, and I'm afraid he won't bother to eat the pea.  And since his problems seemed to start with starvation, I'm especially afraid to deprive him.
Any help you can give me would be much appreciated.  It would also be helpful to know if it was the food deprivation that started this or something else.
Thank you!
Kiesha Messina  

Answer
Hello Kiesha-

Sorry if this response seems short, but I am just getting ready to leave on Thanksgiving Break.

Anyways,
I don't think food deprivation is the entire cause of his troubles. It seems almost like an sudden environmental change shocked him, perhaps a sudden drop in water temperature, or a bad water change on the part of the pet-sitter?

I would not go with the fasting/pea treatment, since that is used mainly to treat constipation, bloating, or swim bladder problems. Instead, I would opt for a gentler treatment - try adding a small dose of aquarium salt to the tank at each water change (if in doubt of the dosage, go on the light side) and a dose of Melafix daily.

Continue feeding the baby pellets (or you can crush the normal sized ones) and if you can get ahold of some live daphnia, try feeding him a tiny portion.

Heating his tank to 80 F may also help get him back to normal.

Hope this is useful!
-Amber Worman