Do you have hay fever? About 10-30 percent of the worldwide population experiences seasonal allergies, also called hay fever (the medical term is allergic rhinitis) [source: Schmidt]. This usually begins in the spring when trees begin to flower and give off pollen. Pollen is a fine powder that's produced by male conifers (plants whose seeds grow inside cones) and flowering plants. Also called flower sperm, pollen carries the plants' male gametes (reproductive cells) of seed plants to the pistils (the female parts) of the same plant or of other plants of the same species. This enables plants to be fertilized and to produce seeds. Pollen is transported by the wind or by insects such as bees. But pollen also causes an allergic reaction in many people who breathe it in the air.
So how can pollen make you tired? The body's immune system releases a substance called histamine to fight allergies, which can cause inflammation in the nose. This inflammation can lead to nasal congestion, sneezing and a runny nose. All of these symptoms make it difficult to get a good night's sleep. A study found that the more severe a patient's hay fever was, the more likely he or she was to have problems with sleep [sources: Leger, et al., National Sleep Foundation]. Lack of sleep often leads to feelings of fatigue and difficulty concentrating at school or at work. Many seasonal allergy patients also suffer from irritability and depression. Researchers are not yet sure whether these mood changes are additional allergy symptoms or if they are caused by a lack of sleep.
The other reason you may feel tired during "pollen season" is from the allergy medication that you take. Antihistamines fight the runny nose and watery eyes you often get from allergies by calming the histamine reaction your body gives off when fighting something it is allergic to. You may know that old-school antihistamines like Benadryl can make you very drowsy, but even the newer 24-hour antihistamines, like Allegra, Zyrtec and Claritin mention on their warning labels that drowsiness may be a side effect. Some people are more susceptible to this and some medications are more likely to make a person sleepy than others. Zyrtec in particular causes drowsiness in one in six consumers, though it is a faster-acting drug than the other two [source: More].
If you have sleep problems due to your seasonal allergies, try to stay indoors during the day to limit your exposure to pollen and use nasal strips at night to open up your nasal passageways. You should also discuss your sleep issues with your doctor who may be able to help you by switching your antihistamine medication. Get your allergies treated because the better controlled they are, the better you'll be able to sleep.