I am a little nervous now

Things were going so well...
Used it last night and it was at 90% charged when I went to bed. Tried turning it on this morning and it was completely dead.
Checked the settings...accidentally did leave the wifi on, but it was in standby. My iPad does not behave this way...
So, will it really drain overnight, in standby like that, and it's my fault for leaving the wifi on? Or is mine defective?