break out in a cold sweat
US /breɪk aʊt ɪn ə koʊld swet/
UK /breɪk aʊt ɪn ə koʊld swet/

1.
to suddenly start sweating a lot because you are very frightened or anxious
:
•
I always break out in a cold sweat when I have to speak in public.
•
The thought of the exam made him break out in a cold sweat.