Intermittent fasting initially means stress that is not familiar for the body. Sometimes it responds correspondingly: For example, headaches, nausea, circulatory and sleep problems can occur.
Such symptoms usually go away after a short time. It is important to drink a lot! Sometimes it also helps to dissolve ¼ teaspoon of sea salt in a glass of water and drink it.
If the symptoms do not improve noticeably, please consult your doctor.