help needed with sick 'sunflower'

Welcome to GOY Rosie. Did you water it well before transplanting it and did you also water it well after transplanting It sounds like a lot of water but it needs to be wet beforehand so it is ready to put out its roots and take advantage of the fresh water which you add after the move. It also helps if you keep plants in a cool shady area until they perk up and look like their old selves. You have to remember it is an annual (grows from a seed and dies in the same season) and they do not take too kindly to being transplanted when they are so far on in their life cycle. It would probably have survived fine in the original pot as long as you watered it every day. Cut off any lower leaves that do not look as if they will recover and leave it to settle down. Do not forget to water it though. It is a lovely cheery plant.

thanks for the quick and informative reply. I'm going to go outside now to move and water it!. many thaks

it mite be worth putting the pot its in in a bucket of water and as scotsgran sais shade it just for now till or if it picks up.