Thank you very much for your advice.
One very major thing I failed to mention in my initial post was that the air filter was heavily clogged with dust and dirt several days ago, and that's when the problem started. In the past I've always changed the filter monthly and never had any problems with a clogged filter; however, this past month there has been an awful lot of work in my house while my cousin has been painting the interior. A lot of furniture and boxes have been moved in and out of the house so I figure there's been a lot more dust raised than usual.
Unfortunately, I wasn't able to check the unit before the repairman came. After looking at the unit, he said he had both good news and bad. He said that my current problem stemmed from the filter having been extremely dirty, and that the unit was slowly returning to normal -- over several days -- since the filter had been replaced. As proof, he had me feel the very cold pipe coming from the back of my house. (Actually, I've noticed the house very gradually getting cooler the past two nights.) The bad news is that if I want to get the house up to code I will essentially need to replace the attic unit, which would cost me $650 out-of-pocket because I have 2-10 Homeowner's Warranty. He said it would cost me either $3,200 or $3,700 without the warranty.
Among other things he said I needed a new auxiliary pan, a safety float??? switch, duct meds???, quick disconnet, and T-start??? (As you can tell, I had trouble reading his writing.) Also, he recommended A/H replacement. He also mentioned a leaking coil and something about excessive mold. He told he there should never be water in the pan.
Do you feel that everything he's telling me sounds within reason? Once again, thanks for your suggestions.