Undiagnosed or incompletely treated complex sleep apnea patients frequently experience central events while on CPAP or bi-level therapy. These patients often get frustrated with their therapy because they continue to have symptoms such as fatigue, sleepiness, headaches and irritability. This may lead a patient to stop therapy all together because they view it as ineffective. Proper diagnosis is essential for treating patients effectively; but how do you recognize complex sleep apnea?