Can ‘heat hangover’ impact Canadians following last week’s hot weather?

Millions of Canadians were under yellow and orange alerts for heat with advisories last week listed across Ontario, Quebec, Alberta, Saskatchewan and the Northwest Territories.

Canadians who felt last week’s heat wave may now be dealing with a “heat hangover,” a term that is gaining popularity on social media.

Millions of Canadians across Ontario, Quebec, Alberta, Saskatchewan and the Northwest Territories were under heat advisories last week as temperatures reached the mid-30s in some places and the humidex in Toronto reached 48, according to Toronto Public Health.

“Initially when we’re exposed to heat, especially in the first heat wave of the season, we struggle to cope with it,” Glen Kenny, full professor of physiology at the University of Ottawa and university research chair in Human Environmental Physiology, said.

Toronto Public Health reported 39 heat-related emergency room visits from June 30 to July 4, when Environment Canada’s orange-level heat alert was in effect. The highest number of emergency room visits was recorded on July 2, with 15.

Parts of Ontario, Quebec, the Northwest Territories and Newfoundland and Labrador remain under yellow warnings for heat, the most common alert, according to Environment and Climate Change Canada (ECCC). The impacts of a yellow alert are “moderate, localized and/or short-term,” with the orange alert being issued whenever a weather event could have “major” or “widespread” implications.

Although ‘heat hangover’ is not a formal medical term, Dr. Steven Lin, chief of emergency medicine at St. Michael’s Hospital with Unity Health Toronto, stated that the symptoms are real.

“Many people do feel lingering effects after a significant heat wave. Fatigue, headaches, dizziness and feeling generally unwell can persist for a day or two as the body recovers from heat stress and dehydration,” Lin said in an emailed statement to Global News.

“This is caused when there is cumulative dehydration and electrolyte depletion when there is prolonged sweating over multiple hot days and when fluid and electrolyte losses are not fully replenished. It results in lingering fatigue, headache, and cognitive impairment.”

Lin also adds that other symptoms can include “sleep disruption with poor sleep quality and sleep quantity.”

The Canadian Centre for Occupational Health and Safety also states that heat exposure is associated with “trouble with concentration, issues with memory, attention and reaction time, difficulty sleeping, emotional changes such as feelings of anger, depression, stress, or anxiety and behaviour changes such as impulsivity, aggression, or violence.”

As a result, the combined symptoms can emulate the feeling of a hangover once a heat wave passes.

“Think of it as having a neighbour who essentially is playing bass music all day, they’ve got big speakers playing. People say it’s just a stressor, which it absolutely is. Your body is under stress, your central nervous system, your brain, everything is changing, because essentially it leads to fatigue. So that’s what heat stress does.”

Health Canada recommends that Canadians “remember that indoor temperatures can remain warm, even after outdoor temperatures cool down.”

“Continue monitoring the temperature of your home and watching for signs and symptoms of heat-related illness in yourself and others.”

Lin also stated that Canadians “should be mindful and stay hydrated during heat waves and even afterwards.”

“Increase fluid intake proactively and do not wait until feeling thirsty. Staying cool is also important. We can spend time in air-conditioned spaces, use fans or have cool showers. We should also prioritize sleep and recovery.”

“Importantly, we should also check on vulnerable family members, neighbours and friends. Older adults, young children, those with chronic medical conditions and socially isolated individuals are at highest risk. Regular check-ins during and after heat waves can identify early signs of heat illness.”

Kenny also said that “the most important thing” following recovery from a heat wave is a proper diet.

“There’s no question you want to maintain electrolytes and hydration and always hydrate regularly. Because, again, it takes time for your body to actually re-equilibrate when it comes to hydration. Just because you hydrate and drink water and electrolytes during a heat wave doesn’t mean that you actually maintain hydration,” he said.

“I think it’s just no different than recovering from intense exercise, you just need to listen to that body.”

This story was originally published by Global News on July 7, 2026. CityAM Canada is republishing it for our Canadian readers.