probably the energy of the 100% full moon. it was also Valentines and some people view it as an important day. what colour was the candle? if it was pink or red then i would agree it was energy surrounding the day.
could also be a draft. say the candles were in a circle around you and someone opened a door in another part of your house, if your door was open a crack, it would be enough to move the door, creating a sudden draft of air.
i use to have a similar experience when circle casting with my coven. one of the older members was a very energetic leo, when she cast the circle the fire candle would always burn down the quickest. depending on if you use the candles in a spell, protection, or the elements when you meditate, you could of placed more energy into that one unknowingly.
if it was a negative force, you should of felt something else, such as the room was colder by that candle, or the energy was heavy.