Developing regular eating and sleeping habits may seem trivial, but even for healthy people – who eat when they are hungry and sleep when they are tired – maintaining regular habits is an important part of staying healthy. The body is easily trained to anticipate when food will arrive (witness Pavlov's dogs). If your body knows that you will eat every day at noon, it will begin producing stomach acid and enzymes shortly beforehand, which aids digestion. The same holds true for sleep. If you go to bed at the same time every night, your body will naturally get sleepy at that time.
Following a routine can also provide a sense of security and stability that can make other stressful situations easier to handle. Many people with CFS/ME have noticed that there is a “straw that broke the camel's back” effect that comes with the illness. You can tolerate a certain amount of strain, but when the next activity comes along you simply collapse. In most cases, people experiencing this will wonder why they have crashed after doing something they have done before. What they are not taking into account is the other activities they have been engaged in. If you add irregular eating and sleeping habits into the mix, it simply decreases the amount of cushion you will have when other stresses come along.
It is not particularly important when or how you perform your eating or bedtime routines. The idea is to develop a regular and predictable pattern that helps structure your day and minimizes your body's need to adjust to change. The fewer adjustments your body needs to make, the less energy it must expend. Anything that reduces the workload on your body will produce immediate benefits. Your body will have more energy to heal itself, and, by controlling what is within your reach, you will have more energy to deal with those things that you cannot control.