I didn't notice any difference in my level of energy or my tiredness quotient
before being diagnosed with prostate cancer. I haven't read in any literature that it is common for those in the early stage of the disease.
Let me add that it has taken me a full six months to return to my former level of energy and fitness after surgery. I am now back doing my full exercise routine that I have done for the past 10 years--aerobics, weights and stretching. My fitness index (measured by V02max) is where it was before surgery.
Many of us survive prostate cancer, but having had prostate cancer changes us forever.