Fast current at the start makes you anxious (8)
I believe the answer is:
insecure
'anxious' is the definition.
(similar in meaning)
'fast current at the start' is the wordplay.
'fast' becomes 'secure' (similar in meaning).
'current at' becomes 'in' (synonymous in some cases - eg at school, in school. I am not sure about the 'current' bit.).
'the start' is a charade indicator (letters next to each other).
'secure' after 'in' is 'INSECURE'.
'makes you' acts as a link.
Can you help me to learn more?
(Other definitions for insecure that I've seen before include "open to attack" , "Sinecure arranged for the nervous" , "Vulnerable" , "Not firmly fixed" , "Wavering" .)