As long as you stayed in bed for like 7-8 hours, and they probably basically forced you to from my experience with sleep studies (a lot of them), you probably slept more than you realize. I thought for one study that I had been up staring at the clock for hours, and surely I had been, but drifting in and out of sleep throughout the night was enough for them. I guess it should also be kinda stated that they know you're there because you have symptoms that make sleeping different for you than what is expected as the norm. They know no one will sleep perfectly fine under monitored conditions and they can find ways to work with the data they get.