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It is possible that this is a reaction to the heat, such as heat stroke after exerting in the heat, this is likely (chills are a sign of heat stroke).
It is important that you rest.
Can someone help you and apply ice packs to your groin and arm pits? (You may cover the packs so as not to be uncomfortable)
Drinking water is correct, and an electrolyte solution or juice would be suggested.
Can you check your body temp? The goal is to get your temp down to 101 to 102 F (38.3 to 38.8 C).
If you are too weak to do these things, and if you have no one to call and help you, you should call 911.
I am standing by to answer any more questions about this, and to help monitor you if need be. Please reply to the post so I can continue to help you as necessary.