Prolonged overexertion or running out of energy during a workout or race to the point where you're reduced to walking, taking a long break, or stopping entirely - is something no one wants to go through. Two common terms for this most-unpleasant experience are "hitting the wall" and "bonking" and the symptoms are numerous. They include nausea, dizziness, feeling faint, and being overly fatigued. Here are a couple of tips to help prolong endurance and prevent bonking:
Make sure that you "refill the tank" with high quality carbohydrates and protein within the first 60 minutes after all workouts and races. This replenishes and helps increase glycogen stores, providing your body with more ready-to-use fuel for your next workout or race.
Further Reading: Recovery - A Crucial Component for Athletic Success
Don't eat too close to the start of your 60+ minute workouts and races. Doing so will only accelerate the rate at which glycogen stores are utilized, depleting them much more rapidly, which increases the potential for bonking.
Further Reading: Proper Fueling - Pre-workout & Race Suggestions
Consume the appropriate amounts of fluids, electrolytes, and calories during exercise. Dr. Bill Misner states, "Taking too much fluid or too little, too much sodium or too little, and/or too much carbohydrates or too little may contribute to a premature bonk."
Further Reading: Less is Best - The Right Way to Fuel
Do a sensible warmup (not too long or too intense) and start your workout or race at a moderate pace. Going "redline" right from the start will deplete your body's finite glycogen stores very quickly. This increases the potential for premature fatigue or a full-fledged bonk to occur.