A small percentage of men who use Cialis report feeling dizzy and lightheaded after taking the medication. These cases often involve the utilization of other drugs , as can be seen in some side effect reports. Like other ED medications, Cialis can cause nasal congestion. This side-effect occurs in 2-3 3 percent of men who use Cialis and may appear at both a 10mg and 20mg doses. Most of the time, this side-effect can be managed by increasing your water consumption and using over-the-counter antacids.