There is no one set rule about the severity of the symptoms associated with OSA. People with mild, moderate or severe OSA can all experience symptoms of daytime somnolence. However, it has been suggested by NICE (2008) that the risk of cardiovascular problems (e.g. hypertension, cardiovascular disease, respiratory failure, metabolic impairment and ultimately, premature death) is evident in people with moderate and severe OSA. Supporting this, Redline (2002) also found that these associated risks occur in moderate and severe OSA if they are left untreated.