Made to go back in time, Rex gets the jitters (6)
I believe the answer is:
nerves
'the jitters' is the definition.
('nerves' can be a synonym of 'jitters')
'made to go back in time rex' is the wordplay.
I cannot really understand how this works, but
'rex' could be 'r' (common abbreviation e.g. GR=George Rex, King Georg) and 'r' is located in the answer.
The remaining letters 'neves' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
'gets' acts as a link.
Can you help me to learn more?
(Other definitions for nerves that I've seen before include "Bodily fibres carrying impulses of sensation" , "Fibres that convey feelings" , "Bodily fibres that convey sensations" , "Body fibres conveying sensations" , "They connect the brain with other parts of the body" .)