Whether in epidemic and sporadic forms, M.E. is always an acute (sudden) onset disease. Patients are well one day and very ill with neurological and cardiac and other symptoms the next.
The onset of M.E. is frequently very dramatic, M.E. patients can very often tell you not just the day that they became ill, but the exact hour they became ill.
The severe symptoms and significant disability begin on day one in M.E. This is not a gradual reduction in ability levels or a gradual increase in symptoms which occurs over weeks, months or years; it is an acute change. A person is healthy one day and very ill the next.
M.E. expert Dr Byron Hyde explains that:
[The] prodromal phase is associated with a usually short onset or triggering illness. This onset illness usually takes the form of either, or any combination, of the following, (a) an upper respiratory illness, (b) a gastrointestinal upset, (c) vertigo and (d) a moderate to severe meningitic type headache. These are only the most common onset illnesses or symptoms of which there are several. The onset illness is associated with either a low grade or subnormal temperature, headaches, sometimes persisting and accentuated by movement with intermittent attacks of vertigo or dizziness. Evidence of a previous immune insult [such as a recent immunisation] is found regularly in both epidemic and sporadic cases. The usual incubation period of the triggering illness is 4-6 days. The second and third phases of the illness are usually always different in nature from the onset illness and usually become apparent within 1-4 weeks.
The virus that causes M.E. has an incubation period of 4 - 7 days.
M.E. can commonly be diagnosed within just a few weeks, if the doctor has experience with M.E.
To read or download an extended and fully referenced version of the above text, please see the What is M.E.? page.
Additional relevant links:
M.E. is an acute onset illness, however it should be noted that: (a) some sufferers will be unsure of their onset type (they may not recall it, or may not recall it accurately, for various reasons) and (b) in some cases, acute onset M.E. is preceded by a series of unrelated minor infectious episodes (in a previously well patient) which may be misinterpreted as being a gradual onset of the M.E.
(These minor infectious episodes may be due to the immune system being under temporary or chronic stress from events such as; recent immunisation, repetitive contact with a large number of infectious persons, or the effect of travel; as in exposure to a new subset of virulent infections. This pre-existing temporary or chronic immune system weakness is not seen in all patients and is not what causes M.E., although a compromised immune system will of course make the body more vulnerable to all types of infections, including M.E.)
For more information on the viral infection evident at onset in people with M.E., and the outbreaks of M.E. etc. see The outbreaks (and infectious nature) of M.E. page