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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.
The reason we suggest you take something besides water is because of electrolyte balance. If it is hard for you to stomach anything else, you might instead want to add a little juice to the water (dilute the juice) or even try something like any soda type drink you have, which contain sodium at least. Because you were likely sweating, you can get low in sodium, and this can cause some of the symptoms you are experiencing such as the weakness and nausea.
Feel free to follow up with me so that I can know how you are doing, or if you have any other questions. I'd appreciate knowing whether or not you begin to feel better if possible.