Dizziness and fainting
Patients may experience dizziness and fainting [5] during heatstroke, and this is caused by reduced blood flow to the brain. Heat can cause blood pressure levels to drop, which leads to lightheadedness. It can also be brought on by long hours of dehydration. This heat episode is called heat syncope (fainting).
Note that some of these signs and symptoms occur at the early stage known as heat exhaustion. When any of these symptoms last longer than thirty minutes, it is best to see your doctor immediately.
References:
[1] https://www.webmd.com/a-to-z-guides/heat-stroke-symptoms-and-treatment
[2] https://www.mayoclinic.org/diseases-conditions/heat-exhaustion/symptoms-causes/syc-20373250
[3] https://www.medicinenet.com/heat_stroke/article.htm
[4] https://www.mayoclinic.org/diseases-conditions/heat-stroke/symptoms-causes/syc-20353581
[5] https://www.betterhealth.vic.gov.au/health/healthyliving/heat-stress-and-heat-related-illness#:~:text=Dizziness%20and%20fainting%20%E2%80%93%20heat%2Drelated,light%2Dheadedness%20before%20fainting%20occurs.