I am sure you were in a panic. Tropical fish do best if their temperature is stable within a few degrees of their ideal. But most can survive with a drop of, say 20 degrees without dying. Many folks have experienced a broken heater etc.. and it may stress the fish, but by attending to it as soon as possible, it is usually not fatal.
This IS however a good time to point out that this is a good reason to invest in the largest tank you can afford. The water holds heat. A 10 gal tank will cool down quickly to room temperature or a little below, much quicker than a 125 gal tank will. Another thing you can do to insure stable water temp. , is to have large rocks in the tank (stabilized with rods and silicone. Rocks also hold heat. I speak from experience, because my home is NOT on an electric line. We use generator power, and it is shut off every night for 8 - 10 hours. Usually my tank temp. is 76 + F. In the morning it might have cooled down to 72F. We also burn wood to heat the house, and on two occasions since I have had the tank, we have had to go away for 2 or 3 days, with the heat off, and no electricity, the tank was at around 64 when we got home. I never did loose a fish. Now I am fully aware that these fluctuations in temp. can cause stress, and could have resulted in problems, all I am saying is that the best way to moderate all the stress factors in your tank is to have the biggest one you can.
Fish in the Frozen North
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. Your tank should be able to hold heat for quite awhile! I'm glad your fish are ok. 