I just wanted to bring to your attention this article on a laptop that caught on fire and killed a person recently.
There are not a lot of details, but you do have to remember that laptop gets really hot, and has vents for cooling. When the laptop is on a bed or couch, the vent holes are covered, and if it is on a sheet or pillowy surface, the side holes get covered. It can overheat, and cause a fire.
Laptops are almost too hot to put on a lap, and honestly, most people use them on a flat surface such as a desk, which I think it funny they still call them laptops.
There was even a report that came out a couple years ago about men becoming sterile from using laptops because the heat on the "lap" area over-heated the "lap" area and could cause sterility. There is something to that overheating thing.
This is not something to be freaked out about, but it is something to consider when leaving your laptop on where there is not good ventilation.