It really sounds like a obvious thing but dehydration kicks in faster then one might think. Try to drink water regularly during the day. Also stick to raw diet (like vegetables, fruits,...) since they add additional water to your body and it is easier for our bodies to digest.

We are also on a start of a warm-front here in Europe but I guess that is nothing compared to the temperatures and humidity levels in northern India. Hope it will get cooler in the days to come at your place.