6. Rapid heart rate
Having a rapid heart rate after spending a day in the sun can be indicative of something serious. If you are having a rapid heart rate, along with other symptoms, it is a situation which requires urgent medical care.
When it comes to cardiac symptoms, it is always very important to err on the side of caution and be checked out.
7. Mental confusion
People who are experiencing a heatstroke will often feel faint and dizzy, but mental confusion is another sign. If a person is experiencing mental cloudiness and confusion, it could be indicative of a heatstroke.
8. Not producing sweat
One of the main differences between heat exhaustion and heatstroke is that a person stops sweating. If someone has spent too much time in the sun, it is normal to feel hot and sweaty.
However, if a person has developed a heatstroke, there will be a lack of sweat, in spite of feeling extremely hot.
Having a seizure is a very serious symptom of heatstroke. A seizure can present quickly and have few warning signs. If a person has a seizure, it is very important to get them to the hospital immediately, without delay.
10. Extreme headache
If a person has spent a lot of time in the sun and has a bad headache, it may be due to suffering a heatstroke. It is common for people to have a small headache after spending time in the hot outdoors, but if it’s really bad especially with other symptoms listed, you might want to go back inside.
Heatstroke is a preventable condition. According to the Mayo Clinic, there are certain steps a person can take to keep it from happening.  A person should wear lightweight, loose clothing which will not hug the body tightly and retain heat.
It is important to drink plenty of fluids when out in the heat for long periods of time, because it will keep the body well hydrated.
If you notice you are becoming overly hot or displaying any of the warning signs of a heatstroke, it is important to get cooled down and if necessary seek medical attention when warranted.