If your blood sugar drops you might feel tired, irritable and low in mood. Starting the day with a proper breakfast, eating regularly throughout the day and choosing foods that release energy slowly (like rice, oats, whole grain bread) will all help.
A balanced diet should contain fruits, vegetables, protein and healthy fats. Five portions of fruit and vegetables a day help provide the minerals, vitamins and fibre your body needs. For healthy digestion have plenty of fibre, fluid and exercise regularly.
Caffeine is a stimulant--it will give you a burst of energy, but then may make you feel jittery, anxious or crash when your energy levels suddenly drop. Caffeine is in: tea, coffee, chocolate, cola and many other fizzy drinks. Try switching to decaffeinated drinks, especially in the evenings before bed