exhausted runner
18 Feb 2026

Post-Event Hypoglycaemia (Low Blood Sugar) – Adult

by | posted in: Discharge Advice | 0

What Happened Today

You experienced low blood sugar (hypoglycaemia) after your event.

During prolonged or intense exercise, your body uses up stored glucose (sugar) for energy. If intake does not match energy use, blood sugar can fall.

Low blood sugar can cause:

  • Shaking or tremor
  • Sweating
  • Dizziness
  • Blurred vision
  • Confusion
  • Nausea
  • Weakness
  • Feeling faint

Your blood sugar was low when checked. It improved after you had fast-acting carbohydrate (such as glucose, juice, or sports drink, or in some cases, intravenous glucose or glucagon). You are now back to normal.

Common reasons after endurance events include:
  • Inadequate carbohydrate intake before or during the event
  • Delayed recovery nutrition
  • Dehydration
  • Exercising harder or longer than usual
  • Alcohol intake before or after the event
  • Diabetes (if applicable)

In people without diabetes, this is usually a temporary energy imbalance, not a long-term problem.

Glucose is the body’s main fuel source, especially for the brain.

When blood sugar drops:

  • The body releases adrenaline (causing shaking and sweating)
  • The brain does not receive enough fuel (causing confusion or dizziness)

Once glucose levels return to normal, symptoms usually settle quickly.

After an episode like this:

  • You may feel tired for the rest of the day
  • Mild headache or nausea can occur
  • Appetite may increase
  • Symptoms should steadily improve over several hours

It is normal to feel “washed out” after both the race and the low blood sugar episode.

It is not normal to have ongoing confusion, repeated fainting, or persistent vomiting.

For future events:

Before exercise
  • Eat a carbohydrate-containing meal 2–3 hours before racing
  • Avoid skipping meals
  • Limit alcohol beforehand
During prolonged events (>60–90 minutes)
  • Use sports drink, gels, or carbohydrate snacks
  • Aim for regular intake rather than waiting until you feel weak
After exercise
  • Have recovery nutrition within 30–60 minutes
  • Include carbohydrate and protein
  • Continue regular meals for the rest of the day

If you have diabetes:

  • Review your medication, insulin dosing, and fuelling plan with your GP or diabetes team before your next event.

See your GP within 1 week if:

  • This was unexpected and you do not have diabetes
  • Episodes are recurring
  • You had no clear trigger
  • You fainted or lost consciousness

Further tests are sometimes needed if episodes occur without heavy exercise.

🚨Call 000 or go to the nearest Emergency Department (or get your responsible adult to) if:

  • You cannot keep fluids down
  • You become confused or difficult to wake
  • You have a seizure
  • You lose consciousness
  • Symptoms return and do not improve after eating sugar
  • You develop chest pain
  • You have severe shortness of breath
  • You have repeated vomiting
  • If symptoms have fully resolved, routine follow-up is not required.
  • See your GP within 1 week if this was unexpected or recurrent.
  • If you have diabetes, book review within 3–7 days.

In Australia – Healthdirect: 1800 022 222
Alternatively, call or visit your GP or local Emergency Department.

NB: This information has been prepared with reference to the most up to date Australian standards and guidance in relevant sports medicine fields. It is prepared in good faith, however is only intended for use as explicitly directed by a DeployED health practitioner. It does not replace medical advice, nor does it purport to be perfect. If you have any doubts about the advice here, please consult your own doctor. If you have not been sent here by us, then this is not for you and DeployED accepts no responsibility for any outcomes which occur from your use of this information.

Evidence Base: Based on Australian Sports Medicine and Endocrine Society guidance for exercise-related hypoglycaemia.
Version 1.0
Review due: February 2027 (Annual review cycle)

Follow Dr Stuart McLay:

Emergency Physician

Dr Stuart McLay is passionate about the delivery of exceptional care, everywhere. He is the founder of DeployED, a Fellow of the Australasian College of Emergency Medicine (FACEM - an Emergency Physician), a Core trainee of the College for Intensive Care Medicine, and a Mass Gathering Medicine / Expedition Medicine enthusiast. He's also a husband to 1, and father to 3, and a great annoyance to many.