it' usually used to describe a kind of statement when you worry about sth or sb.
[directly translated into English is : your heart is dangling that cannot go back to where it should be]
eg.
Mary;s husband is a soldier in the war, Mary的心一直悬着的/Mary的心悬着没有着落
(Mary's heart keeps dangling/ Mary's heart is dangling. ,[because she worries about her husband] )
:)
here “一颗” can be removed, "悬着一颗心没着落" ,this kind of expression you can only use in the articles because it's too literary)