If you have a bad health there are no reasons why you shouldn't go to Nidlongdir,
The best way to get a better health, is to spend a few days at The Blue Bells Inn in Leafenheim. You will receive the best treatment, and the fairies will do their best to make you feel comfortable no matter what your problem is!
Visit The Rainbow Tower and get help from the spirits
You should also go and visit The Fairy Dust Mill. On your way to Nidlongdir you should go, and see Mother Bog, and ask her for a bottle of healing mist. You will also find lots of healing if you visit the rainbow tower in Apple Hold Castle or Queen Agrafina's white Garden.
On you way back you should visit Danagonia in the caves of Dragonia, and ask her if she has any healing jewelry that might help you! Danagonia will recive human payment if you would like her to send some of her jewelry. She has lived among the humans, and she knows about their way of trading!