What Is Hypoglycemia?

Hypoglycemia means your blood sugar has dropped below 70 mg/dL (3.9 mmol/L). It's the most immediate and potentially dangerous acute complication in T1D. While highs cause damage slowly over time, lows can become dangerous within minutes. That's why understanding hypoglycemia — its levels, causes, and symptoms — is absolutely essential.

The ADA Classification

The ADA classifies hypoglycemia into three levels. This isn't just academic — it determines how urgently you need to act and what kind of treatment you need.

Two Types of Symptoms — Understanding the Difference

Your body sends two different types of warning signals during a low:

Adrenergic symptoms (adrenaline response — your body's alarm): These are your early warning system. Your body detects dropping blood sugar and releases adrenaline:

• Shakiness or trembling
• Sweating (often cold sweats)
• Rapid heartbeat (palpitations)
• Anxiety or feeling of dread
• Hunger (sudden, intense)
• Pale skin
• Tingling around the mouth

Neuroglycopenic symptoms (brain running out of fuel): These appear when your brain isn't getting enough glucose:

• Confusion or difficulty thinking
• Difficulty speaking (slurred words)
• Poor coordination or clumsiness
• Vision changes (blurry, double vision)
• Mood changes (sudden irritability, crying)
• Numbness in lips or tongue
• Drowsiness

Common Causes of Low Blood Sugar

Understanding the causes helps you prevent lows before they happen.

Insulin-Related (the most common cause):

• Too much insulin for the carbs eaten
• Insulin stacking (taking a correction too soon after a meal bolus)
• Injection into a spot with faster absorption (exercised muscle, warm skin)
• Basal rate too high (pump users)

Food & Timing:

• Skipping or delaying meals after taking insulin
• Eating fewer carbs than expected
• Miscounting carbohydrates
• Alcohol consumption (blocks the liver from releasing glucose)

Activity:

• More physical activity than usual
• Exercise without adjusting insulin or adding carbs
• Delayed exercise effect (blood sugar can drop hours after activity)

Other Factors:

• Hot weather (increases insulin absorption)
• Altitude changes
• Gastroparesis (delayed stomach emptying)
• After recovering from illness (insulin sensitivity increases)

Scenario: Marco's Late-Night Low

Marco, 22, plays basketball with friends every Tuesday evening. He's figured out his pre-game routine — he reduces his dinner bolus by 30% and has a snack before playing. But tonight, he goes to bed at 11 PM with a blood sugar of 130 mg/dL and wakes up at 2 AM drenched in sweat, shaking, with his CGM alarming at 52 mg/dL.

What happened? The delayed exercise effect. Intense physical activity can keep pulling glucose into muscles for 6-12 hours after you stop. Marco's blood sugar was fine at bedtime, but his muscles kept absorbing glucose while he slept. His alarm saved him — this is exactly why CGM low alerts are so important, especially on exercise days.

Marco's lesson: On basketball nights, he now sets a temporary lower basal rate for 6 hours after exercise (pump users) and has a 15-20g protein + carb snack before bed. He also sets his CGM low alert to 80 mg/dL on those nights instead of his usual 70 mg/dL.

Hypoglycemia Comparison Card

Hypoglycemia Unawareness — A Special Risk

Some people with long-standing T1D lose their early warning symptoms over time. This is called hypoglycemia unawareness — your body stops releasing adrenaline at the usual threshold, so you don't feel the shaking, sweating, or hunger. Your first symptom might be confusion or poor coordination, which means you're already at Level 2.

If you suspect hypoglycemia unawareness:

• Talk to your healthcare team immediately
• Consider a CGM with low alerts (if you don't already use one)
• Aim for a period of strict avoidance of lows — this can help restore awareness over weeks to months
• Your targets may need to be adjusted temporarily