Hello bluedisc,
an increase in heart-rate is by no means unusual and the shaking or nervousness is usually a result of the withdrawal from stimulants such as coffee, tea, condiments or even alcohol.
THE PULSE

"The pulse varies greatly during a fast. It may run up to 120 or even higher, or it may drop as low as 40, per minute. Indeed, Mr. Macfadden records a case in his practice in which the pulse went down as low as 20 and was so feeble it could scarcely be felt. It is the usual thing to have the pulse rate increase at the beginning of the fast and then, after a day or two, to drop. In chronic cases that are confined to bed during the fast, the pulse usually, after its temporary rise, drops to 48, or 40, where it may remain for a day or two days and then mounts up again to 60. After a few days it will settle at 60 and remain there until eating and activity are resumed. It is, of course, understood that the pulse is subject to all the variations, while fasting, as at other times of life, and that where there is "disease" of the heart, or nervous troubles, it will often vary greatly from the above standard. Where stimulants are employed during a fast, these occasion more heart activity than if taken when one is eating."

http://www.soilandhealth.org/02/0201hyglibcat/020127shelton.III/020127.ch27.htm

The heart rate going up is a normal response to fasting I would imagine. The cirulation system is vital of course to the fasting system. It is important both in the breaking down of fats and other stores and 'digesting' them through ketones and also in the release of toxins which have also been stored by the body while not fasting and unable to expell them. It is likely that the increased heart rate is just due to the fact that the circulation system is the focus of the fast at that particular time. At other times it could be the liver, or the bowels, the body follows a list of 'repairs' in the order necessary to heal the body most quickly and efficiently.

The release of old toxins back into the bloodstream can also cause similar effects to the ones they had when you first ingested them. Caffeine is a perfect example. It could well be a combination of the caffeine and the increased need for toxins to be released through the blood that is causing your heart to work harder. Toxins can also cause worse symptoms such as headaches etc if you are susceptible to them, they will all pass once the toxins have passed out of your system through the bowels, sweat glands or even the lungs.

So it sounds like you're doing fine. Good luck continuing. :)

Andrew.