Some people find that they cannot get to sleep at night during the summer unless their room is ice cold. Which is somewhat funny since some of these same people insist on being nice and warm during the winter. Anyways, it is important to make sure that you are not over doing it when it comes to sleeping with an air conditioner on at night. Fresh air is always best but if you cannot sleep with your window open for safety concerns or fears than go ahead and stick with the air conditioner. Just make sure that the room does not get too cold though.
You would be surprised how many people will end up with a cold in the middle of a hot summer because they slept in a room that got below forty degrees. In order to make sure that the room does not get too cold, you might want to look into a temperature controlled air conditioner.
There are window units that allow you to punch in the exact temperature that you want and then the unit will shut off when it gets to that temperature instead of continuing to make the room colder. As the room heats up some, the air conditioner will kick back on in order to get the temperature back to your desired setting.
These window air conditioner units usually cost a little bit more but not by much. If you want to make sure that you have a comfortable night of sleep without freezing to death, these are the air units to go for.