Mark - I had a similar problem about a year ago. Try taking a
combination of potassium and a supplement 5HTP. WalMart MAY carry it
at a considerable savings (like one half). I still take it today and
when I don't I get that "brain fog" feeling.

It worked for me!

Sorry, all I can say is this:

Carb Withdrawal (canned response)

Have you started a low carb diet within the last few days? Do not be
surprised if you start to feel achy "flu-like" symptoms early on in
your low carb WOE. The most common time for these symptoms to hit is
around days 3-5, though they have been reported as early as
day 2, and have lasted into the beginning of the second week. People
have reported feeling light-headed, weak, headachy, ill, feeling like
they are going to pass out, like they have "been run over by a
steamroller".

It seems to be a side-effect of your body switching from carb-burning
mode to fat-burning mode. If you are trying to give up caffeine at
the same time your symptoms may be compounded but people who try to
pass if off as only caffeine withdrawal are wrong because many folks
who had already given up caffeine sometime in the past, or who chose
not to give up caffeine when starting LC, also have the same symptoms.

Typical symptoms include:
nausea, achiness, dizziness, tiredness, lightheadedness, trembling,
blinding headaches,depression

If you experience this you are not alone, but are a very typical new
low carb dieter. The good news is that it is temporary, and most people
report that by the end of week two they feel better than they have
felt in years!

While nothing seems to alleviate it completely except the passage of
time you can ease the symptoms a bit by drinking plenty of water,
getting your potassium and calcium/magnesium supplements, and taking
some aspirin or ibuprophen if necessary.

Glycogen depletion is one of the factors that sometimes causes someone
who is just starting LC to feel tired.  The initial response to a
switch from high-carb to low-carb is typically a severe glycogen
depletion, until the body achieves a new equilibrium and starts
replenishing the muscles using gluconeogenesis.  This is also
responsible for a large percentage of the initial weight loss.

Debbie

On the one hand, that is a common a symptom of carb withdrawal.

On the other hand, if you are consuming any products with aspartame, try
switching to another sweetener, and soft drinks that use other sweeteners.
A very small number of people report a brain fog like you describe when
consuming aspartame products, myself included.  There is no proof of
the matter, just several anecdotes from people who get foggy from it.

Now, I don't believe the propaganda that claims aspartame breakdown
products "build up" to "toxic levels", because the fact of the matter is
that the symptoms go away after about 36 hours of not using any aspartame.
Either it builds up or it doesn't -- you can't have it both ways and
claim that it builds up, and then report that it suddenly disappears
when you stop using it, which is what most claim.

Usually, the claim is that it's a methanol poisoning, from the breakdown
of aspartame, despite the fact that the breakdown from a can of diet
soda has less methanol than an orange or a tomato.  Also despite the
fact that the foremost symptom of *real* methanol poisoning is blindness
from destruction of the optic nerve.  There is no widespread report of
blindness among people who claim to have "aspartame disease."

My own theory is that I have an unusual sensitivity to free phenylalanine,
or some difficulty in processing it although not actually having PKU --
perhaps especially when consumed in diet soda separately from meals
(which is when amino acid supplements are claimed to be effective,
phenylalanine being an amino acid).  Phenylalanine is involved in some
neurotransmitters.

BTW, none of the different artificial sweetener chemicals are even
remotely related chemically to each other, so a sensitivity or problem
with one of them does not imply that one will have a problem with other
artificial sweeteners.