The sleeping thing is the key to understanding the whole performance art piece. The whole thing was about our obsession with pop stars and idols, so much so that we want to know about EVERY little detail of their lives.
Think back to 2007. People followed Britney around LA for HOURS, as she got gas, went to Starbucks, McDonalds, etc. Everything was photographed and written about and obsessed over. If people could have watched Britney sleep, they would have. She was metaphorically on the biggest stage in the world for that whole year during her breakdown. Everyone watched everything.
So tonight, Gaga put that on a literal stage. People tend to forget that Britney got a tattoo on the back of her head the same night she shaved it. She turned the decay of celebrity, the iconic image of a troubled star shaving her head as a cry for help, into a piece of art... It's literally taking place in a museum, after all.
She doesn't think you're going to be fascinated and thrilled watching her sleep for two hours. She's doing that specifically so you think, why the hell are we so obsessed with our icons that we sit here and watch them sleep?
She knows people are going to think this means she's out of ideas and that her time's up... So she literally put a "15 minutes of fame" countdown clock onstage with her, having already reached its end. She's a step ahead of you. Always.