msjproper,
If we were just talking about the heater I would not be all that concerned. I assume your house is in the general area of 70 degrees (give or take a few degrees) The tank will cool down to the temperature in the room overtime but it should take a little while. A month or so ago I forget to plug my heater back in after a water change
and realised that a week or so later and did not loose any fish (and that was my salt tank) IMO The temperature change will not outright kill any fish but it will add stress to an already stressed tank. Will this be just over the limit - no one can really tell. It sounds like you have been having some problems with the tank. Ick can be hard to eradicate but I am sensing that it might be more than that. Do you know what your water parameters are. The ammonia, nitrite, nitrate, levels and anything else you may know from the water test would help us help you. A brief history of the tank and the contents etc. would also be useful. You said they recommended a 25% water change which was your first one in 2 1/2 years. That seems like a very long time which may be contributing to water quality issues and causing some of the apparent problems. How long have you been battling ick and what are using?
In terms of a heater they see ones that clip on the back with the control unit that sits out of the water (I suspect that may be what you had). For a few dollars more you can get one that is submersible so the whole unit goes in the water including the control and a wire comes out. I prefer these for many reasons but the one that jumps to mind now is that you can mount it horizontally about two thirds down in the tank. With the exception of massive water changes you do not encounter the problem that you just did. (You also do not have to remember to plug it back in - my personal challenge) They also trend to be just a bit more rugged and durable in all regards.
It sounds like you are dumping a lot of chemicals into the tank. Often times the folks at the store suggest this because it is money for them. IMO most problems need to be addressed at the root cause and not just keep treating the symptoms which many of these chemical do. I also shy away from many of the meds because they can accumulate and become toxic if overused. That said I probably would not change my routine tonight. Often times a rapid change is more harmful than any given condition
Most people when they start out make a few mistakes. All you can do is learn from them. I know I had my share of disasters. Don't get too discouraged
I have a 36 gal fresh water tank, I just got water water tested and was told to do a 25% water change. I asked all nescessary questions as this is the first time I have done so, I had them walk me through at the store. We had a big problem, apprenently they must have forgotten to tell me to unplug everything. Now I realize this is commen knowledge, I did not unplug the heater and it burt and shorted out. I did get all of the parts out before it went to far, but no I am out of a heater. What shall I do now? How do I get the water temp up. I also have ick in my tank and scaleless fish, that I am treating, so temp is very important. It is sunday at 8:20, no one is open to get one. Any suggestions? I am sick over what happened.
Sorry to hear about your problems
help 
