Since my humidifier broke down (overheated I think), these past few days' humidity has been as low a 35% at midnight.
I didn't know I coudln't sleep well under low humid environment until the time I moved to New York, apparently. Dry throat, deep voice (I can sing bass everytime I wake up like this).
Solution: I tried bowls of waters around back in Stony Brook. Either get a new humidifier or put a wet tower around. It seems this occurs only within a week's span a year at this latitude.