ZACH: Dude, can you chill out about your freaking elevenses ’til we get this song straightened out?
BRIAN: I’m hypoglycemic. If I don’t get something in my system, I’m gonna crash.
Hypoglycemia, the medical term for low blood sugar. Hypoglycemia may result in headaches, tiredness, clumsiness, trouble talking, confusion, fast heart rate, sweating, shakiness, nervousness, hunger, loss of consciousness, seizures, or death. It is usually caused by taking medications used to treat diabetes, such as insulin.
People sometimes use the word in a non-medical sense, to mean that they feel a bit faint or dizzy because their blood sugar has dropped due to not eating for a while. This is called “postprandial syndrome”.
The Annotated Gilmore Girls 