Looks like early dehydration
Welcome to XXXXXXX
Please check out for these symptoms - dry mouth/eyes, dry and mildly wrinkled kind of skin, delayed reflexes, taking time to understand verbal communication etc. If any such symptoms are there then take him to hospital.
If feeling sleepy looks odd, then his regular routine then this can also be sign of early dehydration.
If none of these symptoms are there then continue giving him fluids and he will improve in few hours.
Give him fluids with salt and sugar in it.Maintain a cooler environment around him.
Hope this helps.Please ask if there are doubts.Regards.