What you're talking about here pud's friend sounds like a pseudo-exacerbation.

A pseudo-exacerbation is a temporary inflammation of a nerve already damaged by a prior flare. They can lead to the same type of symptoms that a full exacerbation causes, but in a pseudo flare, the symptoms will only last 24 hours or so.

Pseudo-exacerbations are usually caused by temperature rises, and can be triggered by fevers (as in those caused by infection), by the environment (e.g., sun exposure, a hot bath), or exercise (e.g., mowing the lawn). Once the cause is removed, symptoms quickly disappear.

Although the word "pseudo" brings to mind "fake," the symptoms are quite real. The major differences between a true exacerbation and a pseudo-exacerbation is the time the symptoms last, and the latter does not represent any progression of the disease. No new lesions will be formed during this time.

Here's one of many articles about the condition: http://www.healthcentral.com/multipl...67078/24256/ms

Hope that helps.