You'll definitely want a filter of some type or let some fresh air in more often.

Another thing you may want to consider is changing your mattress. A bed is an incubator for dustmites and their feces.

According to the American Lung Association, around 50-80% of asthma and hayfever are triggered due to infections from dust mites.

Read more about [URL="http://www.essentiadirect.com/research/dust-mites"]dust mites here[/URL].