Inclusion Criteria: (Cohort 1)  Male and female patients age 18 or older at the time of consent Have a permanent address in the United States for the duration of the study Have an email address and access to the internet for the duration of the study Able to provide unassisted informed consent Medical Record Consent (optional) Diagnosed with Chronic Fatigue Syndrome (CFS) or Myalgic Encephalomyelitis/ Chronic Fatigue Syndrome (ME/CFS) OR  Report experiencing one or more of the following symptoms (record all that apply):  Greatly lowered ability to perform normal daily activities due to profound fatigue that has lasted for at least 6 months Worsening of (fatigue) symptoms after physical or mental activity that would not have caused a problem before illness (post-exertional malaise). Sleep Problems. Feel overly tired or unrefreshed even after a full night of sleep Problems with thinking and memory (trouble thinking quickly, remembering things, paying attention to details, have "brain fog") OR Worsening of symptoms while standing or sitting upright -  Exclusion Criteria:  Pregnancy  Inclusion Criteria: (Cohort 2)  Male and female patients age 18 or older at the time of consent Have a permanent address in the United States for the duration of the study Have an email address and access to the internet for the duration of the study Able to provide unassisted informed consent Medical Record Consent (optional)  Exclusion Criteria:  Pregnant Diagnosed with Chronic Fatigue Syndrome (CFS) or Myalgic Encephalomyelitis/ Chronic Fatigue Syndrome (ME/CFS) OR  Report experiencing one or more of the following symptoms (record all that apply):  Greatly lowered ability to perform normal daily activities due to profound fatigue that has lasted for at least 6 months Worsening of (fatigue) symptoms after physical or mental activity that would not have caused a problem before illness (post-exertional malaise). Sleep Problems. Feel overly tired or unrefreshed even after a full night of sleep Problems with thinking and memory (trouble thinking quickly, remembering things, paying attention to details, have "brain fog") OR Worsening of symptoms while standing or sitting upright