Omar received a diagnosis of lung cancer three months ago. Since then, he has felt nervous and often feels his heart pounding. What might explain omar's symptoms?

The nervousness and heart pounding felt by Omar after he is diagnosed with the lung cancer is can be a result of the anxiety and depression. Major of the patients who are diagnosed with cancer (specifically lung cancer) tend to experience the symptoms of anxiety and depression. Their quality of life changes after the diagnosis. The depression level of the patients increases after the knowledge of the presence of the lung cancer.

Hence, the answer is 'depression and anxiety'.