This prepping and survival idea comes to us from South Korea, due to an unfortunate situation in that nation. The shutdown of six of their 23 nuclear power plants has brought frequent blackouts and high prices for electricity. To survive during the harsh winter weather, some citizens have hit on the idea of using a tent, indoors, to increase the air temperature around them. The heat from your body and your warm breath increases the air temperature in the tent as much as 15 degrees F above the indoor temperature, according to this report: Would you use an indoor tent to save money on heating costs?. Some enterprising souls have gone so far as to place a tent around their bed.
As a prepping idea, the use of a tent indoors is quite clever. Tents are widely available and not too expensive, especially given that a tent used for this purpose does not need to withstand rain or wind. Combine an indoor tent with warm sleeping clothes and a sleeping bag, and you should be much better equipped to handle a power outage in winter, or any disaster that affects your ability to heat your home.
I suppose if an extended blackout in winter leaves you without heat, and you presently lack a tent, you might make an impromptu tent around you bed to obtain the same effect. Just make sure the tent is not air-tight. You want to keep in body heat, but some air flow is necessary.