Have you had the opportunity to discuss your concerns with others being treated for prostate cancer? They might be your best source of information. In my experience, doctors do not know as much about anti-anxiety/antidepressant drugs as they should before prescribing. You are wise to consider the effects of adding an antidepressant before taking one. I would advise against Venlafaxine/Effexor (an SNRI), as it does cause sexual dysfunction and is extremely difficult to discontinue--depending on the dose and length of time on the drug. I have been on it for years and have been trying to get off it for years. I would suggest researching SSRIs, if you decide to go that route. Short-term, an antidepressant might help; typically, it takes weeks for them to have an effect, and effects vary among individuals. These drugs work by altering your brain. Have you tried non-drug treatments for depression/anxiety first? I would recommend all the exercise and physical activity you can manage. You can find other suggestions on this website. I wish you all the best, and hope that you find the solutions you need.