Erectile dysfunction can be due to mental anxiety or physical disorder. According to your age (48) and the organic possibilities for disease (atherosclerosis, for example) ... impotency is a possible diagnosis. Atherosclerosis is a disorder of the blood vessels. You can first request laboratory analyses to check your blood cholesterol, triglycerides, sugar… and to evaluate the possibility of developing atherosclerosis. This may play a part in erectile dysfunction.
Erectile dysfunction is not mentioned as a side effect of Zanex (alprazolam). Alprazolam is a drug used for treating anxiety. Both insomnia and erectile dysfunction could be also due to anxiety. You can consult a mental health doctor for your anxiety and erectile dysfunction and follow up with your primary physician for the other diagnostic tests.