my 6 mth old pup has been sleeping for most of the day and hasn't eaten at all since 3pm yesterday,he's been out for a walk and is going to the toilet normally,but i've just noticed his eyes look really droopy and sad and his breathing is quite quick,this happened about 2 mths ago by the time i took him to the vet he was fine.last time it happened i had been walking him in a particular field near us for a week or two and haven't walked him there since ,until this week when he's been to the same field three or four times(could this be a coincidence?)

I would take him back to the vet - 24 hours is a long time for a normal 6 month to go without food so he must be feeling ill.  It sounds as if he may have a temp. and some kind of infection?