I have a 1 1/2 year old husky, who is normally very energetic, happy and healthy... She has no health problems that I know of.. I have taken her to the vet once in the 4 months or so that I've had her.. though, I did get her from craigslist, from people who gave me no information about whether she had shots(though they hinted that she had, I guess). Anyway, a few days ago, I noticed that she had fleas, so I asked a professional if I could use feline flea meds on her(something like advantix, the kind you rub in between the shoulder blades) since I had some, and didn't have the canine kind, and he said it was fine. I only used one pack of cat sized flea meds... She was acting kind of strange before that, but now, for the past few days, she's been acting depressed and has been lethargic, sneezing constantly. This morning she was happy to go outside, but tonight when I tried to take her, she was frightened to go out... so much so, that she urinated all over the floor when I tried to pull her out with her leash. She is now also scared of my air conditioner. I live on kind of a busy street, and my window unit ac is kind of loud.. could this be something do with her hearing, or.. I don't know? Allergic to the flea meds?? Help? :(

It could be a reaction to the flea medication. Perhaps you should switch to using special shampoo in order to get rid of the fleas. Take the dog off them, and see if the dog looses its stress. It might also be good to check the dog isn't sick.

A cat dose of Advantix is not likely to have affected a husky like this unless he is super sensitive to the chemical.
The lethargy is suggestive of not feeling well.
The reluctance to go outside could be something behavioral or a reaction to something that has frightened him while outside.
Ad far as the air conditioner, perhaps some aversion to the loud noise, it is possible that the latter 2 could be somehow related.
You should get him to the vet to address the lethargy and get him medically sound before worry too much about the behavioral right now, but discuss all these things with your vet.
Good luck I hope you get him sorted out.