When Rich was in PNG, he was doing some pretty hairy dives then too.  He
never did seem to eat very much and had to be reminded to eat quite often!

T©

As an insulin dependent diabetic. . .

Diving runs my blood glucose levels down faster than any other activity,
faster than mowing the lawn, working out, biking, whatever.

My theory is that it is the water temperature, and the body's attempt to
 warm the ocean to 98.6  The colder the water, the faster and greater
my drop in bG level.

With a "normal" person, the liver makes up for dramatic demands on
glucose levels. But if the person has not been eating, or if the demand
has been too great, there can be hypoglycemic symptoms, and I've heard
several comments from non-diabetics, post-dive, of mild and passing
symptoms that are the same as my "low" symptoms (slight dizziness,
slight disorientation, short-lived fatigue).

As Charlie Coughran explains it:

When a normal person starts to exercise (or loses a lot of body heat),
the insulin output of his pancreas goes down. At first blush, this seems
backward since the muscles are working hard and therefore require more
glucose to be transported from the blood into the cells. There are two
reasons more glucose can be transported with less available insulin. The
first is that during exercise insulin becomes much more efficient. The
mechanism of this effect is not fully understood, but it helps overcomes
the reduction in circulating insulin.

Second, exercise activates non-insulin mediated glucose transport
pathways. These pathways are not sufficient to handle the load in the
absence of insulin, but do increase the effective insulin efficiency.

When insulin levels decline relative to the counterregulatory hormones
(glucagon, epinephrine, norepinephrine, growth hormone, and cortisol)
the liver is stimulated to release stored glucose. The blood glucose
that is being transported into the cells is replaced by that from
hepatic stores. It is this hormonal balance system that keeps the
levels of blood glucose in the normal narrow range during exercise.

What we diabetics do is eat carbohydrates timed to arrive at the blood
stream in the form of glucose when it is needed, fast acting
carbohydrates immediately preceding the dive.

Exercise also produces effects at longer time scales. Sometime after
exercise, there is often a take up of blood glucose by the muscles to
replenish depleted stores. This most often occurs an hour or two after
exercise, but has been reported in the range of ½ hour to 48 hours.
Again, as is the case during exercise, artificially high insulin levels
will lead to hypoglycemia. Both diabetics and non-diabetics can
experience hypoglycemia after exercise.