Get well soon, Flame!

I agree, make sure you don't over-medicate because that will stress him out even more. It depends on the illness what kind of treatment you use... if it's bacterial or fungus, you will want to turn OFF the heater and treat with salt and/or anti-fungus meds. Here's a site with a lot of common Betta diseases ~

http://www.bettatalk.com/betta_diseases.htm