https://meassociation.org.uk/what-is-mecfs/

Definition

ME/CFS has long been recognised as a ‘Post-viral Fatigue Syndrome' and neurological condition by the World Health Organisation, NHS and Department of Health.

The National Institute for Health and Care Excellence (NICE) has determined a clearly defined diagnostic criteria and produced clinical recommendations that are aimed at improving life quality. The ME Association endorses the NICE Guideline on ME/CFS and recommend it is read by patients, family members, and carers, and then discussed with healthcare professionals to ensure you are receiving the best standard of care.

Long Covid is being recognised as a ‘Post-viral Fatigue Syndrome' similar to ME/CFS that is triggered by the Covid-19 virus. NICE has produced a Rapid Guideline which is evolving as the evidence-base develops. Long Covid doesn't have a clearly defined diagnostic criteria but recommendations are also aimed at improving life quality.