A reader contacted me about her blood pressure changing significantly from day to day. I said that I would research and prepare a summary of what is known. High blood pressure is known as hypertension and means pressure over 140. Hypotension is the medical term for low blood pressure (less than 90/60).
- ” the mean values for the left ventricular end-diastolic diameters, stroke volume index, and cardiac index as well as the mean blood pressure were all significantly smaller in the ME group than in the Controls.” 
- “As many as [CFS] 50 participants were randomised; mean age 49 (SD 13) years,…. mean baseline office blood pressure 128/78 (18/12) mmHg”  i.e. 17% was over 146.
- ” CFS-POTS patients experienced significantly lower baseline diastolic blood pressure (P = 0.002), significantly higher heart rate and lower pulse pressures at each standing measurement.” 
- “psychological stress contributes …..heart rate, systolic and diastolic blood pressures, and plasma levels of noradrenaline and adrenaline increased during the interview” 
- “Serotonin and noradrenaline reuptake inhibitors… elevated blood pressure” 
- “objectively measured abnormalities of blood pressure variability in CFS and that these abnormalities have the potential to be a bedside diagnostic tool.” 
- Elevated nocturnal blood pressure and heart rate in adolescent chronic fatigue syndrome .
- ” In the control group, but not in the [FM] patients, blood pressure was inversely associated with mental performance. This finding is in line with the well known cognitive impairment in hypertension. The lack of this association in FMS confirms previous research showing aberrances in the interaction between blood pressure and central nervous function in the affected patients.” 
- From 2012
- “The present results extend on our previous work with maximal exercise and show that CFS and CFS + FM differ in their responses to steady-state exercise.” 
- Lower ambulatory blood pressure in chronic fatigue syndrome . “Compared with the control population, the CFS group had significantly lower systolic blood pressure (p < .0001) and mean arterial blood pressure (p = .0002) and exaggerated diurnal variation (p = .009). There was a significant inverse relationship between increasing fatigue and diurnal variation of blood pressure in both the CFS and PBC groups (p < .05).”
- “Gastroesophageal reflux disease (GERD) and irritable bowel syndrome (IBS) patients had lower blood pressure, “
- “[With adolescents]At night (sleep), HR, mean arterial blood pressure and diastolic blood pressure were significantly higher in CFS patients as compared with controls (p < 0.01). During daytime, HR was significantly higher among CFS patients (p < 0.05), whereas blood pressures were equal among the two groups.” 
- “CFS in adolescents is characterized by reduced systolic blood pressure variability” 
- “There is limited moderate evidence supporting Far Infra Red Saunas efficacy in normalizing blood pressure” see this post on Infrared Saunas.
- “cardiovascular effects of probiotics Lactobacillus fermentum CECT5716 (LC40), or L. coryniformis CECT5711 (K8) plus L. gasseri CECT5714 (LC9) (1:1) …exert cardiovascular protective effects in genetic hypertension ” 
Recording blood pressure and pulse is a should do for CFS/FM patients. You should record daily at the same time and average the week to observe any trends. There can be significant variation from day to day. If you are able to do some light steady exercise daily, you should also record the blood pressure every 4 minutes during the exercise(use the above charts for reference). Blood pressure should go up if a treatment is successful.