People react different to changes in temperature and humidity. The exact cause of your sleepiness from dry heater air is very rare, so your question is best answered by a doctor. Many people claim to become sleepy when they are overly hot, but Iíve never heard of anyone becoming sleepy only when it is hot and dry as opposed to hot and humid. However, a number of theories come to mind.
Excessive heat can make you sleepy because you are a warm-blooded mammal. Your body must stay within a limited temperature range for your continued survival. The body compensates for outside temperature in various ways in order to make sure your internal body temperature does not change dramatically.
When it is cold, your body shivers. Shivering creates movement through muscle action that raises your bodyís temperature. When it is hot, you may become fatigued or sleepy because if you move a lot, your body will generate even more heat. If your body becomes too hot, you will eventually suffer from heat fatigue. If your temperature is not corrected, heat fatigue could turn into heat stroke and, eventually, death.
When you are sleeping, your body generates the least possible amount of heat. The reason why you do not get sleepy when it is hot and humid could be because you are not comfortable when it is humid. During high humidity, you will sweat, and the sweat does not evaporate quickly. This leaves you wet and sticky, which is definitely not a very comfortable condition for sleeping.
When it is dry and hot, you still sweat, but your sweat evaporates very quickly. This leaves your skin hot but dry, which is an extremely comfortable state for sleeping.
The only other reason why you may become sleepy from heater air is because something is wrong with your heater or you are using an outdoor heater indoors. Some heaters generate carbon monoxide, a colorless and odorless gas that is extremely poisonous. One of the first effects of carbon monoxide poisoning is become excessively sleepy. You can check the carbon monoxide levels in your home with a simple detector that can be purchased at any store that sells hardware.
Of course, if this also happens in your car, it is probably not the heater. To fix this problem, turn the heat down and suffer the cold or get a humidifier.
Posted 3275 day ago