Inky,
Hypoglycemia is also called "low blood sugar". It's a condition where your body metabolizes carbs and sugar with a bit too much enthusiasm sometimes (by producing a bit too much insulin, which binds with the sugars, which makes them unavailable to your body... But that's probably a little more than you were asking.)
Everybody's blood sugar levels can get really low from time to time, and you've probably experienced some of the symptoms to some degree: weakness/shakiness, dizziness, some sweating, lightheadedness or confusion, blurred vision.
For a doctor to diagnose hypoglycemia, there's a test called a glucose tolerance test. You fast before the test, drink a big glass of a yucky syrupy glucose solution, then give urine and blood samples over the course of several hours. The glucose (sugar) levels in your samples are graphed, and if your sugar levels decrease steadily and gradually, you're normal. If your levels drop more suddenly, the diagnosis is hypoglycemia.
There are lots of degrees of hypoglycemia, from mild to severe. Someone suffering from severe hypoglycemia will have the symptoms occur more suddenly and severely (perhaps to the point of actual blackouts) than those of us with milder problems.
The traditionally accepted treatment for the condition is diet- low carb, high protein, several small meals or snacks a day. The strategy is not to starve your body then suddenly feed it, and not to ingest meals that are extremely high in sugars when you don't also have proteins to metabolize.
For example, if I skip lunch and then have a slice of birthday cake in the late afternoon, I'll probably start feeling really bad 30 minutes later. Shaky, sweaty, lightheaded and grouchy. But if I have a chicken breast and a *small* slice of cake, I'll probably be fine.
Hypoglycemia is not a dangerous condition, it doesn't do any physical damage to your body. And it's certainly much more benign than its distant and very dangerous cousin, diabetes. But it can certainly be unpleasant to live with.
(Diabetes, or "high blood sugar", is caused by too LITTLE insulin, which allows too MUCH glucose to remain in your blood. It is very dangerous and can be deadly when not managed very carefully. Diabetes can cause terrible and irreversible damage to many organs.)
Was this way too TMI? Sometimes I get started and then....
Kathy
(who is not a medical professional, but who has done lots of reading about hypoglycemia over the years...)