I would say that the fan is most likely your culprit. Plants transpire at a much faster rate when wind is blowing on them, causing the leaves to wilt. I would say add a humidifier or lower the setting on the fan. Im not sure what the temp is in your room, but if it can be raised with no problems, u could try raising the temp a little. The warmer the air is, the more humidity it can hold. The moisture holding capacity of air doubles with every 20 degree increase in temp.