Fever
Like lethargy and fatigue, fever is also a non-specific symptom of ankylosing spondylitis. Generally, inflammation anywhere in the body can release certain pyrogenic (fever-causing) substances in the blood. These travel to the brain and affect the hypothalamus, the temperature regulating organ in the body and cause the body temperature to rise.
With AS, you might feel a mild fever that ranges between 99-100F. It usually follows a step ladder pattern and may rise and fall several times in a single day. Many patients got it settled by taking NSAIDs and other anti-pyretics before going to the physician.