I can't find statistics on this but I find it worrying that lap-tops continue to be used in beds and on top of soft furnishings. Laptops have fans that draw in air to cool components when they are in use. In scenarios where there is dust, lint, dried skin, fluff, hair, etc in the surrounding environment, these will be drawn in and can block the cooling pathways or even the fan itself.
My first suggestion is not to use laptops in this way and the second, as a regular maintenance step with the laptop powered off, is to vacuum clean the fan intake port (usually a grille on the side or bottom of the chassis).
Check leads and transformers (the block in the middle of the mains lead) for cracks or damage and change any that don't look up to snuff. Also, my pet hate in these devices is the 13 amp fuse in the mains plug. Ditch and replace it with a 3 or 5 amp fuse.