Temperature in CFS is often reported as low, or very very low. This tends to be ignored by most medical professionals — they have been trained to deal with high temperatures (fever) and not low temperatures.
- “Adolescent patients with chronic fatigue syndrome have abnormal catecholaminergic-dependent thermoregulatory responses both at rest and during local skin cooling” 
This is sometimes called Wilson’s Temperature Syndrome (reading Wikipedia is recommended, his model is suspect). A study on 7 CFS patients in 1998, found that the temperature was normal during the study (37C or 98.6F ) but with CFS patients having almost twice the variation of controls. This increased variability was reported again in 2001. A 1996 study found “the CFS patients showed no significant correlation between the timing of the temperature acrophase and the melatonin onset (P < 0.5), whereas the normal significant correlation was observed in the controls (P < 0.05).”
Another blogger (Dr. Hansa) has written about temperature in CFS, so I will not repeat their material here. Cites like WebMD does cite low body temperature ((below 97.6F or 36.5C) as a common symptom which occurs in some patients. Also it is in Dr. Berne’s Symptom Checklist on Phoenix Rising. It appears to apply only to a subset of CFS patients.
First, let us understand how body temperature works:
“Chronic stress is known to affect serotonin (5HT) neurotransmission in the brain and to alter body temperature. The body temperature is controlled in part, by the medial preoptic area (mPOA) of the hypothalamus.” 
Looking at hypothalamus and “chronic fatigue syndrome”, we find over 150 articles on PubMed. On serotonin “chronic fatigue syndrome” , we find over 100 articles. Both aspects have abnormalities with CFS.
- In myalgic encephalomyelitis/chronic fatigue syndrome, increased autoimmune activity against 5-HT is associated with immuno-inflammatory pathways and bacterial translocation. 
- Increased autoimmune activity against 5-HT: a key component of depression that is associated with inflammation and activation of cell-mediated immunity, and with severity and staging of depression.
No effect found The effect of ondansetron, a 5-HT3 receptor antagonist, in chronic fatigue syndrome: a randomized controlled trial. For a more detail [technical] description see this 2011 article.
Interesting, there are sexual differences with 5HT which may be connected with the difference of incidence of CFS between males and females. 
- Insomnia Caused by Serotonin Depletion is Due to Hypothermia.  – which has implication on sleep issues with CFS.
I am one of those patients whose temperature decrease with increased severity of symptoms. A temperature of 95.5 F (35.3C) was not unusual. As I recovered, the temperature slowly increased. The key is to make sure that you record the temperature at the same time and in the same circumstance each day. There is daily variation in temperature as the day goes on.
The bacterial translocation as a factor does bring us back to gut bacteria dysfunction. The low temperature is a symptom that can be used to monitor you state.