There are also acute and chronic types of fatigue. Acute fatigue is generally short-lived, sudden in onset, and relieved by rest. Chronic fatigue lasts a long time (usually six months or longer), may be insidious in onset, and is usually not relieved by rest.
How common is fatigue?
Among people living with HIV and AIDS, the prevalence of fatigue is quite high. In two studies, 54 and 67 percent of people reported fatigue as a symptom at some point during their course of disease. People with HIV are more likely to suffer from fatigue that interferes with their daily activities than people not infected with the virus. One team of researchers found that when compared with persons not infected with HIV, those with HIV were more likely to be unemployed, to feel fatigued for more hours of the day, to sleep and nap more, and to have a lower level of morning alertness.
Even among people living with HIV, the prevalence of fatigue differs: those with more advanced disease (lower CD4 cell count and/or history of opportunistic infections) are more likely to experience fatigue.
What causes fatigue?
There are numerous possible causes of fatigue among persons with HIV infection. Often, a person with fatigue has several problems that can interact to cause this symptom. Here are possible causes of fatigue:
A Phase III , randomised, 12 month clinical trial (CS21) in prostate cancer  compared androgen deprivation with one of two doses of degarelix or the GnRH agonist, leuprolide . Both degarelix doses were at least as effective as leuprolide at suppressing testosterone to castration levels (≤ ng/mL) from Day 28 to study end (Day 364). Testosterone levels were suppressed significantly faster with degarelix than with leuprolide, with degarelix uniformly achieving castration levels by Day 3 of treatment which was not seen in the leuprolide group. There were no testosterone surges with degarelix compared with surges in 81% of those who received leuprolide. Degarelix resulted in a faster reduction in PSA levels compared with leuprolide indicating faster control of the prostate cancer. Recent results also suggest that degarelix therapy may result in longer control of prostate cancer compared with leuprolide.