Express sorrow at mental problems (6)
I believe the answer is:
lament
'express sorrow' is the definition.
(I've seen this before)
'mental problems' is the wordplay.
'problems' is an anagram indicator (I've seen 'problem' mean this).
'mental' anagrammed gives 'LAMENT'.
'at' acts as a link.
(Other definitions for lament that I've seen before include "Dirge; bewail" , "Bemoan, bewail" , "Mourning song or poem" , "Mourn (a person's death)" , "Mourn in mental way (6)" .)