No. That's not normal. If you have Push notifications turned on for email and if you have multiple email accounts on the iPad that will drain the battery a little faster. Any notifications will drain the battery a little faster. Other than that, when the iPad is in sleep mode, the battery shouldn't drain at all overnight.
I get about 9-10 hours a day out of a full charge. I charge my iPad every night because I use it all day long and it needs a charge by the end of the day.