One after another in accident and emergency (6)
I believe the answer is:
tandem
'one after another' is the definition.
'in accident and emergency' is the wordplay.
'in' indicates the answer is hidden within the clue.
'TANDEM' is hidden in the letters of 'accident and emergency'.
(Other definitions for tandem that I've seen before include "Bicycle for two riders" , "it's not normally what one rides" , "Two-person bike" , "Bike with two saddles" , "Bike for two cyclists" .)