So, it’s very good that you are interested to know more about this and I’m really sorry about your brother, you can stay calm everything, will be okay I’m sure. So first of all you asked what really this is, the heat stroke is a condition where body suffers because it comes in contact with a very high temperature, and when the body temperature is really high your body starts to feel bad (high body temperature is called hyperthermia). When your body receives a high temperature then obviously it is changing the body temperature too so your body start to lose water and this creates shock. Another thing that you have to know is that it can happen not just in summer and not just because of the sun, it happens every time your body receives or goes in contract with high temperature for a very long period. You can ask me why this doesn’t happen when we are at the beach. Well, this can happen but you have to stay more under the sun, in the case of your brother everything happened because he was moving and increased his blood pressure. When a person sweats it’s very important to drink a lot of water in order to fill in the body’s gaps, in the case of your brother he played for some hours and I’m sure he didn’t drink a lot of water to feel the water gaps and to protect the body from the stress he has went through.
When a heat stroke happens to a person you have to call the doctor immediately and don’t forget to tell him all the details, for example how many time the patient have been under the sun and for example what he have eaten during the day. In internet are explained a lot of things that you can do in order to help, but I have heard about so many different situations in which a person wanted to help but did the opposite, that’s why I consider that this is a doctor’s job. If you really what to help, then the first thing, check the person and help him to drink a lot of water, sprinkle his face with a little water, and moisten his forehead with water, the water shouldn’t be very cold, just a little colder than his body temperature. This is what you can do while you are waiting your doctor. Anyway it will be better to prevent these things, there are a lot that you can do for this, and it’s just taking care about yourself and to stay away from the strong sunlight at least during the afternoon and don’t forget to wear a hat, heat stroke ain’t fun, you should take care of it. Hope I helped you in any way with a little information.