The UK has declared a national emergency over the scorching heatwave, with forecasters predicting temperatures will top 40C for the first time on record.
Health officials have warned fit and healthy people could fall ill and even die as a result of the extreme heat.
While the country is on high alert over the heatwave, the Covid pandemic has not gone away.
Britons not feeling well in the heat may be uncertain about the cause. There is some overlap with symptoms of heat-related illness and Covid-19, including a high temperature, headache and loss of appetite.
If someone is suffering from heat exhaustion, they may also feel dizzy, confused, very thirsty and sick.
This can also lead to excessive sweating, pale and clammy skin, fast breathing, a fast pulse, high temperatures of 38C or above, headaches and cramps in the legs, arms and stomach, according to the NHS.
This is not usually serious if the person can be cooled down within 30 minutes, for example by moving to a colder area, drinking plenty of water and lying down with their feet slightly raised.
But heatstroke is more serious than heat exhaustion and should be treated as an emergency.
This happens when the body is no longer able to cool itself down when it gets too hot, which can lead to dizziness, a temperature of 40C or above and not sweating even when feeling too warm.
Other symptoms include headaches, feeling restless or confused, a pulse that is “full and bounding”, becoming less responsibe quickly and hot, flushed and dry skin, according to St John’s Ambulance.
The NHS says to call 111 if someone has signs of heatstroke including feeling unwell even after resting in a cool place for 30 minutes, not sweating despite feeling too hot, a high temperature of 40C or above and feeling confused.
With symptoms including fast breathing or shortness of breath, seizures, a loss of conciousness or not being responsive, 999 should be called instead.
While there is some overlap with Covid, this virus can also cause chills, a continuous cough and a loss or change to smell and taste.
Covid symptoms also include a sore throat, runny or blocked nose and diarrhoea, according to the NHS.
Most people in England now have to pay for a Covid test if they want to check whether they have the virus.
