Bit feverish, getting into bed to relax (3,4)
I believe the answer is:
sit back
'relax' is the definition.
(sitting back is a kind of relaxing)
'bit feverish getting into bed' is the wordplay.
'bit' becomes 'i' (resembles t, a binary digit or bit).
'feverish getting' becomes 'tb' (I can't explain this - if you can you should give a lot more credence to this answer).
'into' indicates putting letters inside.
'bed' becomes 'sack' (e.g. 'in the sack').
'i'+'tb'='itb'
'itb' inserted into 'sack' is 'SIT BACK'.
'to' acts as a link.
Can you help me to learn more?
(Another definition for sit back that I've seen is " Choose not to become involved".)