Charge up to bed with it! (5)
I believe the answer is:
debit
'charge' is the definition.
(I know that charge is a more specific form of the action debit)
'up to bed with it' is the wordplay.
'up' is a reversal indicator (in down clue: letters go upwards).
'to' becomes 'ti' (I can't explain this - if you can you should believe this answer much more).
'with it' means one lot of letters go next to another.
'ti'+'bed'='tibed'
'tibed' in reverse letter order is 'DEBIT'.
Can you help me to learn more?
(Other definitions for debit that I've seen before include "Enter in accounts as sum owed" , "Money owed" , "It's not to one's credit" , "left-side entry" , "Charge" .)