Adrienne,

I googled hyponatremia and breathlessness and, among many others, came up
with this article about athletes having the two:

http://www.wemjournal.org/wmsonline/?request=get-document&issn=1080-6032&vol
ume=013&issue=02&page=0135

Breathlessness is a symptom of hypothyroid. If you're not experiencing an
elevated heartrate or BP, it seems more likely to be a result of *not
enough* hormone replacement rather than too much. So I (and I don't even
play one on tv) would disagree with the doc who told you to lower your meds.
Especially since you weren't having the problem before you lowered your
meds...

It would appear that, if your symptoms coincide with a recent reduction of
thyroid replacement, then that would be the most likely culprit or at least
the most likely place to start.

Here are a couple links to pubmed - articles about Hypothyroid hyponatremia.
You could do a search on pubmed for more articles. I mainly just wanted to
point out that the two conditions are strongly linked.

http://biomed.uninet.edu/2005/n1/musso-h-en.html

A quote from this article: "... Hypothyroidism induced hyponatremia is
classically described as a disturbance secondary to a mechanism alike to the
syndrome of inappropiate antidiuretic hormone secretion (SIADH)5.Some
authors consider that the bases of hypothyroidism induced hyponatremia have
not been yet understood6..." (the authors go on to say that they disagree
with this mechanism, but you get the idea of the gist of the article.)

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_ui
ds=6778601&dopt=Abstract

As a fellow sufferer, I know that most docs won't consider thyroid the
problem if your labs fall within the (extremely broad) normal range - even
if you are symptomatic. However, there are some who treat by symptom rather
than lab value. Maybe you could discuss this annoying development with
whoever prescribed your meds.

Also, perhaps you could just work out indoors (or how about swimming) on
hot, humid days until you get this straightened out?

To your health,

Anne