this is what Shelton has to say re' nausea whilst fasting.............
"Nausea: This seems to be an expression of a sudden decrease of the normal tension of the stomach. It may be induced by a foul odor, a bad taste, a disgusting sight, or an emotional shock. Severe pain, illness, fatigue, rapid descent in an elevator, etc., may produce nausea by lowering the tension of the stomach. These things bring about a loss of tension through a complicated "reflex" mechanism.
Continual emotional disturbances, such as prolonged worries, anguish, grief and repeated shocks, may result in a persistent loss of tone in the stomach and produce the "all gone" sensation or vague nausea often complained of.
In many cases there is no doubt that the sudden withdrawing of all food, as in fasting, results in a temporary lowering of tone or tension in the stomach and this produces nausea. On the other hand, tall, thin, undernourished people are likely to suffer with a chronic lack of tension in the stomach and this becomes more noticeable when they fast. The presence of bile in the stomach also causes nausea. Its presence is very likely to lead to vomiting."
In my own experience this is absolutely the case, and where I suffered from nausea towards the end of my first 25 day fast, and which unfortunately led to intermittent vomiting for several days: the bodys way of expelling toxins and other effluent materials that cannot be utilized as fuel for the body.
Nausea (genuine nausea) is experienced only for a few days, but the all-gone sensation within the abdomen which leads to mild nausea can occur throughout.
Not very pleasant I'm afraid, but extremely beneficial.