Glucose Testing

I'm 30 wks. (as of tomorrow) and I had my first glucose test done today. Where they make you drink the sugar drink and sit in the lobby for an hour then take your blood. Well, I won't get my results until Monday. I feel very tired after drinking the stuff and sitting in the lobby, and I'm just wondering. Is that normal "sugar crash" or is it cause for concern? Anyone else experience the same?