Why the **** am i so STUPID!?

Okay,Yesterday i told my girlfriend i was going to lye down at 7PM and told her I'll be back in a hour.. 8 hours later i wake up... shes sad or mad about it she left me a message of her breaking down in tears thinking i am cheating or ignoring her, i explain to her the next day i accidentally fell asleep and she had nothing to worry about, Today it happened again, went to go clean my room at 7:41 PM and just woke up now 1:35 AM shes awake this time and said she'd talk to me about it when she gets out of the shower. We haven't fought ever before! Please Tell me what to do or some advice would be helpful..