This section is from the book "The Hygienic System: Fasting And Sun Bathing", by Herbert M. Shelton. Also available from Amazon: The Hygienic System Vol III Fasting and Sun Bathing.
It is the usual thing for the fasting person to sleep no more than three to four hours out of each twenty-four hours, and this frequently causes worry. Three general causes for this sleeplessness are recognized: (1) It may be due to general nervous tension. The faster cannot sufficiently relax. (2) Sleeplessness is often due to a deficient circulation. The feet become cold and the faster finds it difficult to maintain warmth. A hot water bottle or jug placed at the feet will usually remedy this. (3) The fasting person does not require the usual amount of sleep. In a general sense, the amount of sleep one requires is proportioned to the quality and quantity of one's food. If you are comfortable and relaxed, you may be quite certain that you will sleep as much as you require.
In his narrative, from which I have previously quoted, Mark Twain records the case of one man who went without sleep for twenty-one days at a stretch, noticing during this period of fasting, no desire for sleep and no ill effects from not sleeping. Horace Fletcher frequently pointed out that when he ate less food he required less sleep. The sleeplessness and sluggishness that follow a heavy meal are well-known to everyone. If we are to be mentally alert, we must eat lightly or not at all. Such facts would seem to indicate that the digestion of large quantities of food is an exhausting process.
The faster who does not sleep is likely to fret and fuss about how long the nights are, but he does not feel the loss of sleep. It is true, of course, that all fasters who complain of not sleeping, like all other patients who declare that they never closed their eyes all night, sleep much more than they think they do. I have visited the rooms of fasters who complained of not sleeping and found them fast asleep, only to have them tell me the following day that they "never slept a wink all night."
A few patients sleep more while fasting than when eating. Insomnia victims are especially likely to do this. Fasting is perhaps the quickest and most satisfactory means of remedying insomnia, although there are cases in which it requires six to ten days to secure the sleep. Sinclair says, of his first fast: "I slept well throughout the fast."
I cared for one young man who slept sixteen hours out of twenty-four almost every day of a thirty days fast. Another man, an asthmatic, slept almost day and night for days during and following the fast. But asthma cases, like insomnia cases, having lost much sleep, usually sleep much as soon as fasting brings relief from the dyspnea so that they can sleep.