Let us make it a rule not to use lap top in bed or put computer on bed with blankets and pillows around.
When the lap top is on the bed cooling fan does not get air to cool the computer and may cause fire.
Uneven surface of the bed sheet blocks the air intake. When the laptop is placed on a flat surface i.e. on desk/table, there is a gap between the desk surface and the base of the casing to allow air to flow/suck in through the air intake vent by the cpu fan to cool the cpu.