Don't be put off by this; I suspect its almost a rite of passage or the equivalent of a hazing ritual to see how each new person handles the heat, and it'll happen again next-time new people start.

You should go back the next day more-prepared.

• Wear a full-brimmed sunhat (not a cap)

• Take a plastic water bottle that you can have on you at all times, like a belt holster. Have a second bottle as backup - both should be 600mL to 1L in capacity.

• Drink from that water bottle, frequently. Several times an hour at least, aim to empty the bottles just about Lunchtime when you can refill.
  Personally I like a small squirt of lime in my water, others prefer lemon, sports drink/electrolite powders. Sugared drinks generally don't help with hydration so avoid juices and soft drinks. Cold/chilled is nice but unless you carry a thermos/vaccuum flask, it soon warms up anyway.

• Apply sunblock to exposed skin and rub it in. You may need to reapply at lunch if you sweat it out.

• Wear white or light coloured clothing that is fairly loose-fitting and made of thin cloth. Do not have it tucked in (presuming you're not working around machinery) Consider where the sun hits you most, and perhaps try a long-sleeved shirt instead of a tee shirt.

• Consider wearing some functional sunglasses too - not so much for the heat but its likely bright as well, and reduce eyestrain.

• Get out of the sunlight whenever the opportunity presents itself. Standing in any form of available shade for a moment will help a lot.

• If you have facial hair, consider trimming it to improve air flow.

I bet you weren't peeing a lot either - because all your body fluids were being sweated out through the skin and lost to evaporation. Not needing to piss means you're low on liquids, so chug half a bottle immediately. That's a warning sign, don't ignore it.

As for the workplace - you've learned, demonstrate that you can adjust, and perhaps if you see the signs of someone else suffering in the future you're pre-warned and can help them avoid the unpleasant crash. This demonstrates your empathy and compassion, along with your observation skills and future leadership potential.

Don't be put off by this; I suspect its almost a rite of passage or the equivalent of a hazing ritual to see how each new person handles the heat, and it'll happen again next-time new people start.
Yes, it hit you hard, but now you're armed with better knowledge of the conditions and can come more-prepared.

You should go back the next day more-prepared.

• Wear a full-brimmed sunhat (not a cap)

• Take a plastic water bottle that you can have on you at all times, like a belt holster. Have a second bottle as backup - both should be 600mL to 1L in capacity.

• Drink from that water bottle, frequently. Several times an hour at least, aim to empty the bottles just about Lunchtime when you can refill.
  Personally I like a small squirt of lime in my water, others prefer lemon, sports drink/electrolite powders. Sugared drinks generally don't help with hydration so avoid juices and soft drinks. Cold/chilled is nice but unless you carry a thermos/vaccuum flask, it soon warms up anyway.

• Apply sunblock to exposed skin and rub it in. You may need to reapply at lunch if you sweat it out.

• Wear white or light coloured clothing that is fairly loose-fitting and made of thin cloth. Do not have it tucked in (presuming you're not working around machinery) Consider where the sun hits you most, and perhaps try a long-sleeved shirt instead of a tee shirt.

• Consider wearing some functional sunglasses too - not so much for the heat but its likely bright as well, and reduce eyestrain.

• Get out of the sunlight whenever the opportunity presents itself. Standing in any form of available shade for a moment will help a lot.

• If you have facial hair, consider trimming it to improve air flow.

I bet you weren't peeing a lot either - because all your body fluids were being sweated out through the skin and lost to evaporation. Not needing to piss means you're low on liquids, so chug half a bottle immediately. That's a warning sign, don't ignore it.

As for the workplace - you've learned, demonstrate that you can adjust, and perhaps if you see the signs of someone else suffering in the future you're pre-warned and can help them avoid the unpleasant crash. This demonstrates your empathy and compassion, along with your observation skills and future leadership potential.