Diabetes is a condition defined by high blood sugar. Whether it’s type 1 or type 2, the core problem is the same: glucose builds up in your bloodstream instead of getting into your cells where it’s used for energy. A fasting blood sugar of 126 mg/dL or higher, on two separate tests, is one of the standard thresholds for diagnosis. That said, low blood sugar is also a common and sometimes dangerous part of living with diabetes, not because of the disease itself, but because of the medications used to treat it.
Why Blood Sugar Rises in Diabetes
Your body relies on a hormone called insulin to move glucose out of your blood and into your cells. In type 1 diabetes, the immune system attacks the cells in the pancreas that produce insulin, so your body makes little to none. In type 2 diabetes, your cells gradually stop responding to insulin properly. Your pancreas compensates by pumping out more and more of it, but eventually it can’t keep up. In both cases, glucose stays in the bloodstream and accumulates.
This is why diabetes is fundamentally a high blood sugar condition. The diagnostic tests all measure how much glucose is circulating in your blood. A normal fasting blood sugar is below 100 mg/dL. Between 100 and 125 mg/dL is considered prediabetes. At 126 mg/dL or above, it’s diabetes. Another common test, the A1C, measures your average blood sugar over roughly three months. Normal is below 5.7%, prediabetes falls between 5.7% and 6.4%, and diabetes is diagnosed at 6.5% or higher.
Where Low Blood Sugar Fits In
Low blood sugar, or hypoglycemia, isn’t part of diabetes itself. It’s a side effect of treatment. When you take insulin or certain other diabetes medications, the goal is to bring high blood sugar down into a safer range. But sometimes the medication pulls blood sugar too far in the other direction. This can happen if you take too much medication, skip a meal, drink alcohol, or get more physical activity than usual.
Several types of diabetes medications carry a higher risk of causing low blood sugar. Insulin is the most common culprit. Certain oral medications that stimulate the pancreas to release more insulin can also drop blood sugar too low, particularly when combined with each other. The risk is real enough that people on insulin often check their blood sugar multiple times a day to avoid it.
How High and Low Blood Sugar Feel Different
The symptoms of high and low blood sugar are distinct, and recognizing the difference matters because the responses are completely different.
When blood sugar is too high, the symptoms tend to develop gradually. You may feel unusually thirsty, need to urinate more often (especially at night), and feel tired. These symptoms can be subtle enough that some people live with high blood sugar for months or years before getting diagnosed.
Low blood sugar, by contrast, tends to hit fast and feel alarming. Common signs include:
- Shaking or trembling
- Sweating
- Rapid heartbeat
- Feeling anxious, irritable, or confused
- Sudden hunger
- Weakness or drowsiness
- Numbness or tingling in the lips or tongue
If blood sugar drops very low, the situation becomes an emergency. Severe hypoglycemia can cause confusion, loss of consciousness, and seizures. It can require help from another person to treat.
Treating a Low Blood Sugar Episode
The standard approach is called the 15-15 rule: eat 15 grams of fast-acting carbohydrate (a few glucose tablets, half a cup of juice, or a tablespoon of sugar), then wait 15 minutes. If you still don’t feel better after 15 minutes, eat another 15 grams. The idea is to raise blood sugar quickly without overcorrecting and sending it too high. Once blood sugar stabilizes, eating a small snack with protein or complex carbs helps keep it steady.
What Sustained High Blood Sugar Does Over Time
The reason diabetes management focuses so much on keeping blood sugar in range is that chronically elevated glucose damages the body in ways that accumulate over years. The main targets are small blood vessels and nerves throughout the body.
In the eyes, high blood sugar can damage the tiny vessels that supply the retina, leading to vision problems and, in severe cases, blindness. In the kidneys, the damage can gradually reduce their ability to filter waste, potentially progressing to the point where dialysis or a transplant is needed. Nerve damage is another common consequence, causing pain, burning, tingling, or loss of feeling, most often in the hands and feet. Nerve damage can also affect digestion, bladder function, and sexual health.
These complications don’t happen overnight. They develop over years of blood sugar running above target ranges. This is exactly why the A1C test, which captures a long-term average, is so central to diabetes care.
Target Blood Sugar Ranges
For most people with diabetes, the CDC recommends aiming for 80 to 130 mg/dL before meals and less than 180 mg/dL two hours after starting a meal. These targets give you a practical window. Staying within this range most of the time significantly reduces the risk of long-term complications while also lowering the chance of blood sugar dropping too low.
Your individual targets may differ based on your age, how long you’ve had diabetes, and what other health conditions you have. But these ranges give a useful baseline for understanding what “in range” means day to day.
Why Blood Sugar Can Spike Overnight
One pattern that confuses many people with diabetes is waking up with high blood sugar despite not eating anything overnight. Two things can cause this. The first, called the dawn phenomenon, happens because your body naturally releases hormones like cortisol and growth hormone in the early morning hours. These hormones raise blood sugar as part of the normal wake-up process, but in diabetes, there isn’t enough working insulin to counteract the rise.
The second, called the Somogyi effect, is a rebound. If blood sugar drops too low during the night (often from too much evening insulin), the body responds with a surge of hormones that push blood sugar back up, sometimes overshooting dramatically. The result looks the same on a morning reading, but the causes and solutions are different. Checking blood sugar in the middle of the night, around 2 or 3 a.m., can help distinguish between the two.
High and Low Blood Sugar Emergencies
Both extremes can become medical emergencies. On the high end, two serious conditions can develop. Diabetic ketoacidosis occurs most often in type 1 diabetes when the body, starved of insulin, starts breaking down fat for fuel and produces toxic acids called ketones. Symptoms include fruity-smelling breath, nausea, vomiting, stomach pain, and fast, heavy breathing. The other condition, hyperosmolar hyperglycemic state, is more common in type 2 diabetes and involves blood sugar climbing to extremely high levels, causing severe dehydration, confusion, drowsiness, and sometimes coma. Both conditions start with the same early warning signs: excessive thirst, frequent urination, and fatigue.
On the low end, severe hypoglycemia that causes loss of consciousness or seizures requires immediate help from someone else, often in the form of an emergency injection that raises blood sugar rapidly. This is why many people on insulin carry some form of emergency treatment with them.