Hydrangeas can suffer from sunburn, but that's more of a scorched look. The leaves will go crispy brown and fall off. The curling you describe sounds more like aphid damage, although they're not a common pest on Hydrangea. Look closely at the tops and bottoms of the leaves and along the stems to see if you can find any small insects. Even if you do find aphids, killing them won't help the damaged stems to recover this year. You'll probably just have to prune off and dispose of the contorted parts. One of the best (and surely the safest) control for aphids are ladybugs. You may be able to buy ladybugs at your local garden center. They're also available online.