Posted: 10/05/2015 at 13:10
Hi Suzy. Have you replaced some of the compost each year and done the usual with feeding and watering? Wilting is more likely to be dry conditions rather than wet, but if it feels heavy, and therefore waterlogged, it might be worth taking it out and making more holes (if possible) or using a different container. It may also be needing potted on into a bigger one. The usual advice is to go only a little bigger each time. There may also be pest damage from something like vine weevil. The creamy white curved larvae are the culprits and if that's the case, you'll see them if you take it out the pot. They eat through the roots and can cause a plant to suddenly wilt. Potted specimens are more vulnerable than those planted in borders.
Hope that gives you a few ideas just now to think about. As you say, it's a lovely plant and it would be a shame to lose it.
A pic would also help with advice if you're able to post one. The little green tree icon in the toolbar above the window you type in is for adding pix.