Question Title: Long term effects of encephalitis

Lacking more details about what happened your husband in such distant
past (23 years ago), it is rather difficult to explain his current
symptoms. However, these combination of symptoms, i.e. headache, nausea,
generalized weakness upon moderate physical activity certainly deserves
further medical investigation. The specific cause of these symptoms
might not necessarily be neurological. For instance, his cardiac
condition might also require some investigation. I would recommend that
he should be seen by your family or primary physician as early as
possible.

This information is provided for general medical education purposes only.
Please consult your doctor regarding diagnostic and treatment options.