Upset, hot and cold, tense: I feel irritation (4)
I believe the answer is:
itch
'feel irritation' is the definition.
'itch' can be an answer for 'irritation' (an itch irritates you). I'm unsure of the 'feel' bit.
'upset hot and cold tense i' is the wordplay.
'upset' shows that the letters should be reversed in order.
'hot' becomes 'h' (common abbreviation eg on taps).
'and' means one lot of letters go next to another.
'cold' becomes 'c' (eg on taps).
'tense' becomes 't' (grammatical abbreviation).
'h'+'c'+'t'+'i'='hcti'
'hcti' back-to-front is 'ITCH'.
Can you help me to learn more?
(Other definitions for itch that I've seen before include "Yen" , "Longing; anag. of 19" , "Strong desire to do something" , "Tickling sensation of skin" , "cause irritation" .)