Without sufficient energy intake, the body can experience hypoglycemia. People often forget to eat or bring enough food on long or difficult routes, or they underestimate how long and exhausting a descent can be.
Typical symptoms for hypoglycemia are shivering, a drop in physical performance, poor concentration, confusion, and impatience. Other symptoms may include nausea and sudden pangs of hunger.
If you recognize these symptoms, rest for a while and have something to eat. The sugars most quickly absorbed into the blood are monosaccharides (simple sugars) such as glucose or energy gels that can be absorbed directly via the mucous membrane in the mouth. You should then eat a couple of granola bars or a sandwich.
Once the food has been digested, physical condition should gradually improve. The hypoglycemic person should make the decision as to whether climbing can continue or the tour should be brought to an end.