Sudden anxiety with satyr-like character in charge (5)
I believe the answer is:
panic
'sudden anxiety' is the definition.
'with satyr-like character in charge' is the wordplay.
'with' means one lot of letters go next to another.
'satyr-like character' becomes 'pan'.
'in charge' becomes 'ic'.
'pan' put next to 'ic' is 'PANIC'.
(Other definitions for panic that I've seen before include "Take fright, lose the head" , "Losing one's head" , "mass hysteria?" , "Frenzy" , "Lose one's cool" .)