Across the UK, temperatures have plummeted below freezing, with widespread frost and fog affecting large swathes of the country. In the north of England and Scotland, snow is expected to fall this week and temperatures might fall to -8C in some areas.
An amber cold health alert has been issued by the Met Office and the UK Health Security Agency, and will stay in place until Tuesday 5 December. The alert was issued because average temperatures are forecast to be 2C (35.6F) or below, and means the impact of cold temperatures will be "felt across the whole health service for an extended period of time, with potential for the whole population to be at risk".
Dr Agostinho Sousa, Head of Extreme Events and Health Protection at UKHSA, said: "With a risk of widespread overnight frosts and some snow across the country this week, it’s important to check in on the wellbeing of those most vulnerable to the cold.
"Cold weather can have a serious impact on health, particularly older people, and those with pre-existing health conditions, as it increases the risks of heart attacks, strokes, and chest infections. If you have a pre-existing medical condition or are over the age of 65, it is important to try and heat the rooms where you spend most of your time in, such as your living room or bedroom."
With that in mind, many of us will be wondering whether we should leave the heating on overnight during colder conditions. Here's what you need to know.
Should you leave the heating on overnight when the temperature drops?
When deciding whether to leave the heating on at night time, it's useful to know what temperature experts advise your home should be in winter.
The Energy Saving Trust states the thermostat in your home should be set to the lowest comfortable temperature (usually between 18C and 21C), while an official report also outlines 18C as the recommended minimum. The vulnerable may wish to heat it slightly higher, and healthy people may wish to heat it slightly less.
And this is similar for overnight.
"It is widely accepted by sleep experts that the ideal temperature for sleep is approximately 18.3C, although we also know this varies slightly person to person," says Nuffield Health physiology national lead, Louise Wright.
"For those over 65 or with pre-existing medical conditions, a systematic review by Public Health England in 2014 stated that maintaining the 18C threshold overnight may be beneficial to protect health, alongside the use of sufficient bedding, clothing and thermal blankets or heating aids as appropriate."
For babies, The Lullably Trust advises that a room temperature of 16-20C – with light bedding or a lightweight, well-fitting baby sleep bag – is comfortable and safe overnight.
How does the temperature at night affect your health?
Being too hot, or too cold, will disrupt your body's ability to get a good night's sleep and keep you healthy.
"A person's core body temperature is regulated by the circadian rhythm," explains Wright. "This means, like our hormones, it rises and falls over a 24 hour period. At night the core body temperature should drop slightly, coinciding with the release of the sleep hormone melatonin, and this signals that the body is preparing and ready for sleep.
"The body starts to cool itself through the process of vasodilation, allowing the blood flow to move away from the core towards the extremities (and this is why you sometimes experience hot feet and hands at night!)."
But, Wright adds, "If where you are sleeping is too warm however, this can interfere with your body’s thermoregulation and therefore cause discomfort and restlessness, as well as a decreased amount of time spent in the restorative stage of sleep."
Overall, it's generally thought to be better to be too cold, than too hot, while trying to sleep, but as you obviously don't want to suffer the implications of shivering through the night, consider whether it's important for you individually to keep your bedroom heated to the 18C minimum, or whether you can stay warm in other ways.
Products to help you stay warm this winter
Silentnight Comfort Control Electric Blanket | £35.56 (Was £42.99) from Amazon
Wearable Hot Water Bottle | £25 from Amazon
Fogarty Superfull 10.5 Tog Duvet | £35 from Dunelm
Teddy Bear Cream Long Hot Water Bottle | £14 from Dunelm
Heatgen Plus Fleece Thermal Leggings | £16 from Marks & Spencer
Heatgen Plus Fleece Thermal Turtle Neck Top | £16 from Marks & Spencer
Thermal Medium Warmth Long Sleeve Vest | £20 from Marks & Spencer
Light Warmth Thermal Long Johns (2 Pack) | £28 from Marks & Spencer
Read more about staying warm this winter:
The exact date you should turn your heating on this year, according to an expert (Yahoo Life UK, 6-min read)
23 ways to stay warm without turning on the heating this winter (Yahoo Life UK, 5-min read)
Martin Lewis' tips for keeping heating costs down in winter (Yahoo Life UK, 3-min read)