I heard you are beset by a sort of milder hysteria (8)
I believe the answer is:
delirium
'hysteria' is the definition.
(synonyms)
'i heard you are beset by a sort of milder' is the wordplay.
'heard you' becomes 'u' (commonly used in online communication. I am not sure about the 'heard' bit.).
'are beset by' indicates putting letters inside ('beset' could historically mean 'cover').
'a sort of' indicates an anagram.
'i'+'u'='iu'
'milder' with letters rearranged gives 'delirm'.
'iu' put within 'delirm' is 'DELIRIUM'.
Can you help me to learn more?
(Other definitions for delirium that I've seen before include "Febrile mental confusion" , "state of ecstasy" , "Disturbed state of mind during a fever" , "Temporary state of mental confusion" , "Extreme mental disturbance" .)