I can second this theory! When I lived in England, I had a crappy room (windows didn't fully close etc) and had LOTS of SPs (no LDs though, because it freaked me out because I didn't know what it was XD). Now I'm back in Belgium in a lovely apartment, where it's always comfortable and I have more trouble reaching SP. I didn't link the temperature to the lack of SP though! So I'll just try sleeping without heating tonight!