Adjective
sick at heart (not generally comparable, comparative sicker at heart, superlative sickest at heart)
(idiomatic) Despairing, distressed, or anxious.
In public Nansen praised Amundsen; in private, according to biographer Roland Huntford, he was "sick at heart". Source: Internet
I think of you day and night and sometimes feel so sick at heart that I believe I cannot bear it any longer. Source: Internet