Heat exhausation can look like light-headededness, extreme fatigue or nausea.
There are other signs of heatstroke as well, including a high body temperature, confusion, slurred speech, a racing heart rate, a change in sweat, headaches, and red skin. Slow down, take a break, or just call it quits if you're not feeling well!
You shouldn't push through any symptoms in order to finish your workout, as heatstroke can be a serious condition that can damage your brain, heart, kidneys, and muscles. Take it easy in the days following any of these symptoms.
Also be mindful of any medications that can affect how your body responds to hydration and heat levels. Especially if you take medications that narrow your blood vessels, regulate your blood pressure, rids your body of water and sodium, or reduce psychiatric symptoms (such as antidepressants or antianxiety medications).