There is nothing more aggravating than waking up with a nose bleed or a sinus headache, especially when an air purifier is present. An air purifier is supposed to clean the air so that you can breathe better and not have to worry about allergens. Getting a headache, pain in the sinuses, or a nose bleed can all be caused by an air purifier. Don't worry though, because the unit is working properly. Other factors are contributing to the issues you are having.
If you're using an air purifier in a high elevation you are more likely to get nose bleeds than someone in a lower elevation. Air purifiers recycle air while running it through some sort of filter (HEPA is the best). Then it pushes out brand new air. As your elevation increases the air decreases. This is why when you ride an elevator or drive up a large hill your ears pop. In order to prevent or, at the very least, ease a bloody nose or congestion, try a lower setting on the air purifier.
The same principle that goes for a high elevation also applies to dry air. If you live in an area where you have a strong current of desert air, then you are more likely to get sinus headaches and nose bleeds. There is little to no moisture in the air and the air purifier, during its recycling process, takes what is left. This dries out the air even further, which causes your sinuses to dry out. There are two solutions. The first is trying a lower setting on the air purifier, and the second is to add a humidifier to inject moisture to the air.
When it's humid you get that sticky feeling all over your body. The air purifier recirculates the air and creates a dryer environment. The change in the air moisture can cause your sinuses to act up and your nose to bleed. If you're using an air purifier in this weather, you'll also need to use a dehumidifier to first decrease the moisture.
Air Purifier Location
Many people will place an air purifier where they spend most of their time. Unfortunately, when you do this, you also expose yourself to the air purifier for a long period of time. This prolonged exposure can help dry out your sinuses and cause headaches, nose bleeds, and even dizzy spells. You should be particularly careful about having an air purifier right next to your bed, especially if you suffer from sleep apnea. Another location to be careful of in your home is the living room. Many families spend the majority of their normal day in this room. One solution is to adjust the levels on the air purifier so it's not as strong. Another fix to the problem is to use smaller air purifiers and position them all around the house. This way you will avoid one or two high-powered air purifiers in key areas of the home.